Late 1770s-Mid 1780s: Outraged by massive taxation without representation and seeking to gain their independence from Britain, the colonies in America band together to fight against the British in the struggle known as the American Revolution.

1840s: Anxious to gain more land for the young American nation, President James Polk helps to instigate a war with Mexico by sending troops into a disputed borderland. The American victory results in a substantial increase in lands for the United States, although not all Americans support the conflict.

Today: Following unprovoked attacks on the World Trade Center in New York and the Pentagon in Washington, America leads an international war against terrorism. The military conflict, centered in Afghanistan, has wide support from the American public.

Late 1770s-Mid 1780s: Neither of America's initial ruling documents—the Declaration of Independence and the Articles of Confederation— address the issue of...