Answer: The US gained control of the island due to the Spanish-American war and the beginning of American Imperialism.
Step-by-step explanation:
The United States and Spain fought a war over Spain's colonies in the Caribbean. Spain did not want to give the colonies up as they were the remnants of the once great Spanish Empire. The United States entered the war with Spain over public outrage via the yellow press, a form of journalism that often blows a situation out of proportion, using sensationalist titles and exaggeration of events. The press stated that the Spanish were performing atrocities on the Caribbean natives, and many US citizens saw it as their duty to protect the interests of the Americas due to the continued existence of the ideals of the Monroe Doctrine, which stated that the United States would defend the Americas from any outside powers. The final straw was when a US warship known as "USS Maine" exploded off the coast of an island, and while it was a malfunction, the yellow press blamed it on the Spanish and the populace of the United States was infuriated. The war was an overwhelming defeat for the Spanish, so much so that the secretary of the US called it "A splendid little war". This was due to the incredible power of the United States naval fleet, created by its booming economy and immense production of resources such as steel. Spain seceded Cuba, Puerto Rico, and the Philippines from the US. However, these regions were not given independence and remained under US control for many years, marking the beginning of the United States' imperialistic policy and marking the end of its isolationist policy.
(you can copy and paste this, its not plagiarized from anywhere.)