What is the capital city of the United States?

The capital city of the United States is Washington, D.C. This designation reflects the city's role as the center of the federal government, housing important institutions such as the White House, the U.S. Capitol, and the Supreme Court. Washington, D.C. was specifically chosen for its location along the Potomac River and for its intention to serve as a neutral ground that is not part of any state, allowing it to symbolize the unity of the nation.

In contrast, New York City, although historically significant as the first capital of the United States under the Articles of Confederation, is not the current capital. Philadelphia served as the temporary capital during various periods in the early days of the Republic, particularly while Washington, D.C. was being established. Los Angeles is a major city known for its entertainment industry but has no role as the capital. This context reinforces the fact that Washington, D.C. is the center of national governance and is why it is the correct answer.