War is generally defined as a violent conflict between states or nations. It has shaped humanity's history, its social and political institutions, its values, and ideas. In the 18th century, America had to fight for its independence, engaging in a war that subsequently defined the nation and prompted the signing of the Declaration of Independence in 1776. Since then, the United States of America has become embroiled in some of the world's most destructive and controversial conflicts.
To learn about the wars the US has gotten involved in and why, including the recent conflict in Yemen, click through the gallery.