What is the american expanison?
The second half of American expansion is the imperial era of the United States, starting with the Spanish-American War in 1898 and continuing, some would argue, until today. After the 1899 Treaty of Paris ending that conflict, the US came into possession of Puerto Rico, Guam and the Philippines, as they were formerly Spanish colonies. This was the birth of the American Empire.
Its growth continued as Roosevelt declared the Carribbean Sea an "American lake" in the Roosevelt Corollary, and in the years following, the US intervened militarily time and time again in countries like Cuba, the Dominican Republic, Nicaragua and Honduras. We also established the Panama Canal as US held property, increasing our strategic reach as an empire.
Finally, during World War II, we held on to islands in the Pacific Ocean we had seized from Japan, including parts of the Marianas.
This pharase could refer to many things because the United States has expanded many times in its history.
The first major expansion of the US came when the US (under President Thomas Jefferson) bought the Louisiana Purchase from France in 1803.
The next major expansion came in 1846 when the US made a treaty with Britain establishing that the Pacific Northwest was US territory.
After that, the US expanded in 1848 with the taking of the Southwest from Mexico in the Mexican American War.
This general trend (as well as the movement of settlers into these areas) is generally known as American expansion.
You can also talk about what was done in the late 1800s as expansion -- taking places like Puerto Rico, Hawaii, Samoa and the Philippines.