United States

Mississippi River: bargeA barge on the Mississippi River near Baton Rouge, Louisiana.Ron Chapple Studios/Thinkstock

Air traffic has experienced spectacular growth in the United States since the mid-20th century. From 1970 to 1999, passenger traffic on certified air carriers increased 373 percent. Much of this growth occurred after airline deregulation, which began in 1978. There are more than 14,000 public and private airports, the busiest being in Atlanta and Chicago for passenger traffic. Airports in Memphis, Tennessee (the hub of package-delivery company Federal Express), and Los Angeles handle the most freight cargo.

air distances from United StatesEncyclopædia Britannica, Inc. Wilfred Owen The Editors of Encyclopaedia Britannica

Government and society

Constitutional framework

The Constitution of the United States, written to redress the deficiencies of the country’s first constitution, the Articles of Confederation (1781–89), defines a federal system of government in which certain powers are delegated to the national government and others are reserved to the states. The national government consists of executive, legislative, and judicial branches that are designed to ensure, through separation of powers and through checks and balances, that no one branch of government is able to subordinate the other two branches. All three branches are interrelated, each with overlapping yet quite distinct authority.

The Mall, looking east toward the Capitol, Washington, D.C.© Peter Gridley/FPG International

The U.S. Constitution (see original text), the world’s oldest written national constitution still in effect, was officially ratified on June 21, 1788 (when New Hampshire became the ninth state to ratify the document), and formally entered into force on March 4, 1789, when George Washington was sworn in as the country’s first president. Although the Constitution contains several specific provisions (such as age and residency requirements for holders of federal offices and powers granted to Congress), it is vague in many areas and could not have comprehensively addressed the complex myriad of issues (e.g., historical, technological, etc.) that have arisen in the centuries since its ratification. Thus, the Constitution is considered a living document, its meaning changing over time as a result of new interpretations of its provisions. In addition, the framers allowed for changes to the document, outlining in Article V the procedures required to amend the Constitution. Amending the Constitution requires a proposal by a two-thirds vote of each house of Congress or by a national convention called for at the request of the legislatures of two-thirds of the states, followed by ratification by three-fourths of the state legislatures or by conventions in as many states.

In the more than two centuries since the Constitution’s ratification, there have been 27 amendments. All successful amendments have been proposed by Congress, and all but one—the Twenty-first Amendment (1933), which repealed Prohibition—have been ratified by state legislatures. The first 10 amendments, proposed by Congress in September 1789 and adopted in 1791, are known collectively as the Bill of Rights, which places limits on the federal government’s power to curtail individual freedoms. The First Amendment, for example, provides that “Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.” Though the First Amendment’s language appears absolute, it has been interpreted to mean that the federal government (and later the state governments) cannot place undue restrictions on individual liberties but can regulate speech, religion, and other rights. The Second and Third amendments, which, respectively, guarantee the people’s right to bear arms and limit the quartering of soldiers in private houses, reflect the hostility of the framers to standing armies. The Fourth through Eighth amendments establish the rights of the criminally accused, including safeguards against unreasonable searches and seizures, protection from double jeopardy (being tried twice for the same offense), the right to refuse to testify against oneself, and the right to a trial by jury. The Ninth and Tenth amendments underscore the general rights of the people. The Ninth Amendment protects the unenumerated residual rights of the people (i.e., those not explicitly granted in the Constitution), and the Tenth Amendment reserves to the states or to the people those powers not delegated to the United States nor denied to the states.