The United States' acquisition of the Philippines, Puerto Rico, and Hawaii are all examples of late-nineteenth century

I am guessing this is multiple choice, if not, I believe the answer would be Imperialism. The definition of Imperialism means: a policy of extending a country's power and influence through diplomacy or military force. Though the United States did not use military force directly against those islands, we got that land fighting with the Spanish (which is using military force.)

So in short, the answer is Imperialism.