Why did the u. s try to control its a affairs Puerto rico

Puerto Rico is a commonwealth of the United States. The US government started to control Puerto Rico in 1898, when the Spanish American Civil war gave the US its control. However, Puerto Ricans struggled to obtain more democratic rights during many years. The US controls the island, but it doesn't interfere with local government policies. American interests on Puerto Rico are based on political as well as economic reasons. The US makes use of Puerto Rico ports and roads. Besides, it also trades sugar and tabacco. Furthermore, US tries to keep Puerto Rico under its control in order to maintain its presence in the Caribbean as well as protecting the Panama Canal.