Answer: After the Civil War the U.S started expanding the control on the Americans staying in other countries of the world.
Step-by-step explanation:
Economic reasons: The industrialization actually increase the need of trade in the late 1800s. US imported sugar from Cuba and silk from china.
Cultural beliefs: Christian religion made itself superior and they sent their missionaries to other countries of the world to elaborate the territory of the Christian religion.
Political ambitions: After the Civil War, the military power was used to protect the native Americans.