After the Spanish-American War, attitudes towards Cuba in the United States were somewhat mixed. Some wanted to annex the country and some wanted to make it independent.
The US decided to establish a military government to rule Cuba for a while. After that, another Cuban Government would take over.
Written by Elihu Root, Secretary of War, the Platt Amendment was introduced into the Senate by Orville Platt. It was passed in Washington, and reluctantly accepted by the Cuban Constitutional Convention, which saw it as the only way to sovereignty.
The Platt Amendment did several things. It gave the United States Guantánamo Bay as a naval base and allowed the US to enter Cuba if it felt things were out of control.
This would be used to insure the country's government remained friendly to the US and that American companies wouldn't be hurt by some sudden change.