The United States government was created by the Constitution, which went into effect in 1789. It is a federal form of government, which means that power is divided between the central government and the individual state governments. The government is divided into three branches: the legislative, the executive, and the judicial. The Constitution includes a system of checks and balances that is designed to make sure that all the branches of government work together and that none has more power than any of the others.

The legislative branch

The legislative, or law-making, branch is the Congress of the United States. It has two sections, the Senate and the House of Representatives. The 100 members of the upper house, the Senate, are each elected for terms of six years. Each state has two senators. The leader of the Senate is the vice president of the United States. The 435 members of the lower house, the House of Representatives, are elected for two-year terms. The number of representatives from each state depends on a state's population. Large states have many representatives, while states with fewer people have fewer representatives. The leader of the House is called the speaker. The speaker is a member of the House who belongs to the party in the majority. The speaker is elected to the position by the members of his or her party.

Congress is responsible for writing and passing laws. The Constitution forbids it to pass any laws on matters that are the sole concern of individual states. Its powers are also limited by the right of the United States president to veto, or reject, legislation. Congress may pass a law vetoed by the president if two thirds of its members (290 members in the House and 67 members of the Senate) vote to do so.

The executive branch

The executive branch enforces the laws passed by Congress. The president of the United States heads the executive branch. If the president dies, resigns, or is removed from office, the vice president becomes president. The president oversees the federal government's many departments and offices. There are 15 departments. They are the Departments of State, the Treasury, Justice, Defense, the Interior, Agriculture, Commerce, Labor, Health and Human Services, Homeland Security, Housing and Urban Development, Transportation, Energy, Education, and Veterans Affairs. The heads of these departments are appointed by the president and serve as his advisers. They are known as the Cabinet. The leaders of other offices, such as the administrator of the Environmental Protection Agency (EPA), may sometimes serve in the Cabinet as well. The president can recommend laws, and the Constitution allows him to share with the Senate the power to decide foreign policy.

Although early presidents in practice often had limited power, presidents in the 20th century became more powerful than the Congress. The president holds office for four years. Initially, presidents could serve unlimited terms, but since 1951 they can only serve two. If a president acts contrary to the Constitution or against the law, he can be impeached (indicted) by the House of Representatives and tried and removed from office by the Senate. Andrew Johnson and Bill Clinton are the only two presidents ever to be impeached. No president has ever been removed from office. A bill of impeachment was voted against Richard M. Nixon, but he resigned before a Senate trial could begin. He was the only president to resign from the office.

The judicial branch

The judicial branch, or judiciary, interprets the laws made by Congress. The Supreme Court of the United States is the highest court in the country. It consists of a chief justice and eight associate justices. All are nominated by the president and must be approved by the Senate. The Supreme Court has the power to strike down laws it finds to be against the Constitution. It has been very important in the history of the United States. Among the court's many cases, it has made rulings on such controversial issues as civil rights, free speech, prayer in school, and abortion.

Most cases tried in the federal court system are first heard in the district courts. There are 89 district courts in the 50 states. The District of Columbia and Puerto Rico each have one district court. The president appoints all members of the federal judiciary.