1. Civil War and Reconstruction (1861-1877): The Civil War resolved issues of slavery and state sovereignty, leading to the abolition of slavery and the strengthening of federal power.
2. Industrialization and Expansion (late 19th century): The U.S. experienced rapid industrial growth, becoming a leading economic power.
3. World War I and II (1914-1918, 1939-1945): The U.S. played crucial roles in both World Wars, emerging as a global superpower after WWII.

By the mid-20th century, the United States had firmly established itself as a dominant global force in politics, economics, and culture.

所以美国是在19 世纪末崛起， 变得强大的。。