Since the early 1900's, the US has largely continued to act as an imperialist power up until the early 1990's. The US military has spent time in Cuba, the Dominican Republic, Cuba, Honduras, Nicaragua, Guatemala, and El Salvador to secure US business and political interests. Governments were removed in Chile, Guatemala, El Salvador and Cuba either through engineering elections or by assassination.
Later in the 20th century, Latin America was a Cold War battleground, where the US favored dictators as long as they were anti-communist. Weapons sales and economic aid were given to leaders that were loyal.
The main way that America did this was by taking half of Mexico in the Mexican-American War in the 1840s.
Next, the US took Cuba (in effect) and Puerto Rico in the Spanish-American War of 1898.
After that, the US dominated the area through the application of the Roosevelt Corollary to the Monroe Doctrine. This said that the US had the right to intervene in the area to prevent European countries from doing so. This led to US takeover of various countries to keep them from defaulting on their debts and being attacked by European countries.