The U.S. Constitution defines a federal system of government in which certain powers are delegated to the national government; other powers fall to the states. The national government consists of executive, legislative, and judicial branches that are designed to check and balance one another; all are interrelated and overlapping yet each is quite distinct.

American Eagle.

Since the Constitution was ratified in 1788, there have been 27 amendments to it. The first 10, known as the Bill of Rights, established a number of individual liberties. Notable among the other amendments are the 13th, 14th, and 15th, which abolished slavery and declared former slaves citizens with the right to vote; the 17th, which provided for the direct election of U.S. senators; and the 19th, which effected women's suffrage. The last, 27th amendment to the United States Constitution was adopted in 1992. Amending the Constitution requires a proposal by a two-thirds vote of both houses of Congress or by a national convention, followed by ratification by three-fourths of the state legislatures or state conventions.

The executive branch of the government is headed by the president, who must be a natural-born citizen of the United States, at least 35 years old, and a resident of the country for at least 14 years. The formal responsibilities of the president include those of chief executive, treaty maker, commander in chief of the army, and head of state. In practice, they have grown to include drafting legislation, formulating foreign policy, personal diplomacy, and leadership of his political party. The members of the president's Cabinet - the secretaries of State, Treasury, Defense, Interior, Agriculture, Commerce, Labor, Health and Human Services, Housing and Urban Development, Transportation, Education, Energy, and Veterans Affairs and the attorney general - are appointed by the president with the approval of the Senate; they are described in the Twenty-fifth Amendment as "the principal officers of the executive departments," but much power has come to be exercised by presidential aides who are not in the Cabinet. Thus, the president's Executive Office includes the Office of Management and Budget, the Council of Economic Advisers, and the National Security Council.

The White House.

The legislative branch of the government is the Congress, which has two houses: the Senate and the House of Representatives. Powers granted Congress under the Constitution include the power to levy taxes, borrow money, regulate interstate commerce, declare war, seat members, discipline its own membership, and determine its rules of procedure.

The Capitol.

With the exception of revenue bills, which must originate in the House of Representatives, legislative bills may be introduced in and amended by either house; a bill - with its amendments - must pass both houses and be signed by the president before it becomes law. The president may veto a bill, but a veto can be overridden by a two-thirds vote of both houses.

The House of Representatives is chosen by the direct vote of the electorate in single-member districts in each state, the number of representatives allotted to each state being based on population and the overall total never exceeding 435. Members must be 25 years old, residents of the states from which they are elected, and previously citizens of the United States for at least seven years. It has become practically imperative, though not constitutionally required, that they be inhabitants of the districts that elect them. They serve for a two-year period. The speaker of the House, who is chosen by the majority party, presides over debate, appoints members of select and conference committees, and performs other important duties. The parliamentary leaders of the two parties are the majority floor leader and the minority floor leader; they are helped by party whips who maintain contact between the leadership and the members of the House. Bills introduced by members in the House of Representatives are received by the standing committees, which meet in private executive session and can amend, expedite, delay, or kill the bills. The committee chairmen traditionally have attained their positions on the basis of seniority, but this practice has been challenged. Among the most important committees are those on Appropriations, Ways and Means, and Rules. The Rules Committee, traditionally conservative, has great power to determine which bills will be brought to the floor of the House for consideration.

Each state elects two senators at large. Senators must be at least 30 years old, residents of the state from which they are elected, and previously citizens of the United States for at least nine years. Each term of service is for six years, and terms are so arranged that one-third of the members are elected every two years.

The Senate has 16 standing committees, among which the most prominent are those on Foreign Relations, Finance, Appropriations, and Governmental Affairs. Debate is almost unlimited and may be used to delay the vote on a bill indefinitely. Such a delay is known as a filibuster and in most instances can be brought to an end if three-fifths of the Senate agree. Treaties made by the president with other governments must be ratified by a two-thirds vote of the Senate.

The judicial branch of the federal government is headed by the U.S. Supreme Court, which interprets the meaning of the Constitution and of federal laws. It consists of nine justices (including the chief justice) appointed for life by the president with the consent of the Senate. It has appellate jurisdiction for the lower federal courts and from state courts of last resort if a federal question is involved. The court has original jurisdiction over cases involving foreign ambassadors, ministers, consuls, and cases to which a state is a party.

The Capitol.

Three types of cases commonly reach the Supreme Court: cases involving litigants of different states, cases involving the interpretation of federal law, and cases involving the interpretation of the Constitution. The court can take official action with as few as six judges joining in deliberation, and a majority vote of the entire court is decisive; a tie vote sustains a lower-court decision. Often the minority judges write a dissenting report.

The Supreme Court has often been criticized for its decisions. In the 1930s, for example, a conservative court overturned much of President Franklin D. Roosevelt's New Deal legislation. In the area of civil rights it has received criticism from various groups at different times. After a 1954 ruling against school segregation, Southern political leaders attacked it harshly. Later, they were joined by Northern conservatives. A number of decisions involving the pretrial rights of prisoners also came under attack on the ground that the court had made it difficult to convict criminals.

Below the Supreme Court are the U.S. courts of appeals. Special courts handle property and contract damage suits against the United States (U.S. Claims Court), review customs rulings (U.S. Court of International Trade), and apply the Uniform Code of Military Justice (U.S. Court of Military Appeals). Each state has at least one federal district court and at least one federal judge. District judges are appointed for life by the president with Senate consent. Appeals from district-court decisions are carried to the courts of appeals.

The great majority of the federal government's revenues come from taxes. The most important source is the personal income tax, administered by the Internal Revenue Service. The receipts from corporate income taxes yield a much smaller percentage of total federal receipts. Another small percentage comes from federal excise taxes, but this is offset by the fact that most of the individual states levy their own excise and sales taxes. Federal excise revenues come primarily from taxes on alcohol, gasoline, and tobacco. Social-insurance taxes and contributions constitute another important source of revenue; estate and gift taxes account for only a tiny fraction of the total.

The governments of the 50 states have structures closely paralleling those of the federal government. Each state has a governor, a legislature, and a judiciary. Each state has its own constitution.

All state legislatures but one have two houses, Nebraska's being unicameral. Traditionally, state legislatures have been dominated by rural representatives who may not always be sympathetic to the needs of growing urban areas. Most state judicial systems are based upon elected justices of the peace (although in many states this term is not used), above whom come major trial courts, often called district courts, and appellate courts. In addition, there are probate courts concerned with wills, estates, and guardianships. Most state judges are elected.

State governments have a wide array of functions, encompassing agriculture and conservation, highway and motor- vehicle supervision, public safety and corrections, professional licensing, regulation of intrastate business and industry, and certain aspects of education, public health, and welfare. These activities require a large administrative organization, headed by the governor. In most states there is also a lieutenant governor, not always of the same party as the governor, who serves as the presiding officer of the Senate. Other elected officials commonly include a secretary of state, state treasurer, state auditor, attorney general, and superintendent of public instruction.

Municipal governments are more diverse in structure than state governments. There are three basic types: mayor-council governments, commission governments, and council-manager governments. In the first type, the mayor and the council are elected; although the council is nominally responsible for formulating city ordinances, which the mayor enforces, the mayor often controls the actions of the council. Boston, New York City, Philadelphia, Chicago, and Seattle, Wash., are among those cities having the mayor-council type of government. In the commission type, voters elect a number of commissioners, each of whom serves as head of a city department; the presiding commissioner is generally the mayor. Tulsa, Okla., and Salt Lake City, Utah, are included among the cities with commission governments. In the council-manager type, an elected council hires a city manager to administer the city departments. The mayor, elected by the council, simply chairs it and officiates at important functions. Des Moines, Iowa, and Cincinnati, Ohio, have council-manager governments.

The United States has operated under a two-party system for most of its history. Since the general election of 1856, the major parties have been the Democratic Party, founded in 1824, and the Republican Party, founded in 1854. The most common mascot symbol for the Democratic Party is the donkey. The traditional mascot of the Republican Party is the elephant. Other parties have occasionally challenged these two but without permanent success. Since the Civil War, only one third-party presidential candidate - former president Theodore Roosevelt, running as a Progressive in 1912 - has won as much as 20% of the popular vote. One reason for their failure is that in order to win a national election, a party must appeal to a broad base of voters and a wide spectrum of interests. The two major parties thus tend to be moderate in their programs, and there may often be little difference between them on some issues. Each has a conservative wing, and each has a wing that is considered liberal. The conservative Democrats tend to be more conservative on racial issues, for example, than their Republican counterparts; the liberal Democrats are more radical on economic issues than the liberal Republicans. The national parties contest presidential elections every four years, but, between their quadrennial national conventions, they are often little more than loose alliances of state and local party organizations.

Republican Party.....Democratic Party.

At the state level, political parties reflect the diversity of the population. Large urban centers are more likely to support a Democratic ticket, whereas rural areas, small cities, and suburban areas tend more often to vote Republican. In many states rural areas and smaller towns control the state legislatures, even though the more populous city areas provide the greater proportion of tax revenue. A Supreme Court ruling in 1964 sought to remedy this situation by ordering states to reapportion their legislatures more closely by population. Some states have traditionally given majorities to one particular party. The states of the Northeast (e.g., Massachusetts and Connecticut) and West Coast (e.g., California and Oregon) and some of the Great Lakes states (e.g., New York and Illinois), known as "blue states", are relatively liberal; Democrats are more likely to win there. The "red states" of the South (e.g., Texas and Oklahoma) and parts of the Great Plains and Rocky Mountains (e.g., Kansas, Wyoming, and Utah) are relatively conservative; Republicans are more likely to win there. Alaska is traditionally a "red state"; Hawaii is traditionally a "blue state".

2008 presidential election results map. Blue denotes states/districts won by Obama/Biden, and Red denotes those won by McCain/Palin. Numbers indicate the number of electoral votes allotted to the winner of each state.
NOTE: 2008 presidential election results map. Blue denotes states/districts won by Obama/Biden, and Red denotes those won by McCain/Palin. Numbers indicate the number of electoral votes allotted to the winner of each state. Obama won one electoral vote (from Nebraska's 2nd congressional district) of Nebraska's five.

In elections for president and vice president, voters actually choose among electors committed to the support of a particular candidate, a system called the electoral college. Each state is allotted one electoral vote for each senator and representative in Congress.

The winner of the 2008 presidential election, Democrat Barack Obama, is the 44th U.S. president and the first African American to hold the office. All previous presidents were men of solely European descent. The 2008 elections also saw the Democratic Party strengthen its control of both the House and the Senate. In the 111th United States Congress, the Senate comprises 58 Democrats, two independents who caucus with the Democrats, and 40 Republicans; the House comprises 256 Democrats and 178 Republicans (one seat is vacant).

Barack Hussein Obama takes the oath of office from U.S. Chief Justice John G. Roberts Jr. in Washington, D.C., Jan. 20, 2009, becoming the 44th President of the United States.

The United States has large economic, political, and military influence on a global scale, which makes its foreign policy a subject of great interest and discussion around the world. Almost all countries have embassies in Washington, D.C., and consulates around the country. However, Cuba, Iran, North Korea, and Sudan do not have formal diplomatic relations with the United States. The U.S. is a founding member of the United Nations (with a permanent seat on the Security Council), among many other international organizations.

At center, President Obama, Italy's Prime Minister Silvio Berlusconi, and Russa's President Dmitry Medvedev, react as they take part in a group photo to mark the G20 summit in London on April 02, 2009. Others in the group in the front row are Saudi Foreign Minister, Prince Saud Al-Faisal; China's President, Hu Jintao and Britain's Prime Minister,Gordon Brown. Center left is Turkey's Prime Minister Recep Tayyip Erdogan, Thailand's Prime Minister, Abhisit Vejjajiva is seen top left. At right is South Africa's President, Kgalema Motlanthe while at top right is Ethiopia's Prime Minister, Meles Zenawi.

In 1949, in an effort to contain communism during the Cold War, the U.S., Canada, and ten Western European nations formed the North Atlantic Treaty Organization, a mutual-defense alliance in which they have since been joined by 14 other European states - including Turkey, which straddles the Eurasian border, and some former Soviet states. In an example of realpolitik, the U.S. also established diplomatic relations with Communist countries that were antagonistic to the Soviet Union, like the People's Republic of China during the Sino-Soviet split.

Recently, the foreign policy of the United States has focused on combating terrorism as well as the proliferation of weapons of mass destruction. Calls by a majority of American citizens continue for increased border security against illegal immigration and the shipment of illegal narcotics, with their primary goal the protection of American interests and the safety of U.S. citizens around the world, against such threats as terrorist infiltration at the border with Mexico.

The military forces consist of the U.S. Army, Navy (including the Marine Corps), and Air Force, under the umbrella of the Department of Defense (DOD) with its headquarters in the Pentagon building in Arlington county, Va. A related force, the Coast Guard falls under the jurisdiction of the Department of Homeland Security in peacetime, but is placed under the Department of the Navy (a component of the DOD) in times of war. The United States Department of Homeland Security (DHS), commonly known as Homeland Security, is a Cabinet department of the Federal Government of the United States with the responsibility of protecting the territory of the United States from terrorist attack and responding to natural disasters. The department was was established on November 25, 2002, by the Homeland Security Act of 2002 from 22 existing federal agencies in response to the terrorist attacks of September 11, 2001.

While high-tech weapons items get a lot of billing, the Global War on Terror is very much an infantry war. Firepower overmatch matters in those situations. The M-32 six-shot 40mm grenade launcher is the US Marine Corps' weapon introduced in 2003 to Regimental Combat Team 5, based in Camp Fallujah.

The military of the United States comprises 1.4 million personnel on active duty, along with additional 860,000 personnel in the seven reserve components (456,000 of which are in the Army and Air National Guard). With a strength of 2.26 million personnel (including reserves), the United States armed forces are the 2nd largest in the world. Conscription was ended in 1973, and since that time the United States has had volunteer military forces, though conscription may occur in times of war through the Selective Service System. The U.S. is considered to have the most powerful military in the world, in part due to the size of its defense budget. The United States military budget is larger than the military budgets of the next twenty largest spenders combined, and six times larger than China's, which places second (although it is widely believed that China significantly understates its actual military expenditures). The United States and its closest allies are responsible for approximately two-thirds of global military spending (of which, in turn, the U.S. is responsible for two-thirds). Military spending accounts for more than half of the United States' federal discretionary spending, which comprises all of the U.S. government's money not accounted for by pre-existing obligations. However, in terms of per capita spending, the U.S. ranks third behind Israel and Singapore. As a percentage of its GDP, the United states spends 3.7% on military ($441.6 Billion in the fiscal year 2006). This compares higher than France's 2.6%, and lower than Saudi Arabia's 10%. This is historically fairly low for the United States. However it must be remembered that the figure presented for United States Military spending has dramatically increased since the attacks of September 11th, 2001 and ensuing military operations in Afghanistan and Iraq. In peace time U.S. military spending will gradually decrease. The U.S. military maintains over 700 bases and facilities in more than 130 different countries on every continent except Antarctica.

U.S. Army Special Forces Soldiers scan an area during a recent patrol in Iraq.

The United States military is a hierarchical military organization, with a system of military ranks to denote levels of authority within the organization. The military service is divided into a professional officer corps along with a greater number of enlisted personnel who perform day-to-day military operations. The United States officer corps is not restricted by social class or nobility. United States military officers are appointed from a variety of sources, including the service academies, ROTC, and direct appointment from both civilian status and the enlisted ranks.

The U.S. military also maintains a number of military awards and badges to denote the qualifications and accomplishments of military personnel.

On July 26, 1948 U.S. President Harry S. Truman signed Executive Order 9981 which radically desegregated the military of the United States. Open homosexuals, however, are still barred from serving openly. By law, women may not be put into direct combat; however, asymmetrical warfare has put women into situations which are direct combat operations in all but name.