These trends came to a head in the Spanish-American War. Conflicts had been increasing in Cuba between the Spanish authorities in control and the local citizens. Americans became interested in several abortive uprisings which occurred on the island. The brutal way in which the Spanish had suppressed them incensed the Americans. The violence in Cuba also endangered American life and property--the result of increasing American investments. The public favored intervention, proposing that their Caribbean neighbors should also share in the benefits of democracy. They viewed the Spaniards as an antidemocratic element from the Old World blocking the road to progress in the western hemisphere. The battleship Maine was sent to the Havana harbor ostensibly on a courtesy visit. Its real object was to protect American interests. It was mysteriously blown up, and many of its crew were killed. The cause of the explosion is still unknown. American chauvinists chose to believe that the ship had been deliberately destroyed, and they demanded retaliation. Before long, American troops were sent to "liberate" the Cubans from Spanish oppression. Although the number of Negro troops who participated in the Spanish-American War was small, they fought heroically and contributed significantly to the American victory. The Negro participants served in segregated units. These included the 9th and 10th Cavalry and the 24th and 25th Infantry units. In the battle of San Juan Hill, the Negro cavalry opened the way for the Rough Riders' famous charge which was led by Theodore Roosevelt. Later in the day, the 24th Infantry came up from the rear to support the action. At the end of the war, Spain gave the United States sovereignty over Puerto Rico and, for the payment of a sum of money, the U.S. also gained the Philippines. Spain gave up her sovereignty over Cuba, but its future status was not made clear. American public opinion had become so wed to the cause of democracy in Cuba that the American government felt it could not take direct control of the island. It was deemed necessary to establish a Cuban Republic, but it was obvious that America would exercise considerable influence over it. Early in the century the Platt Amendment was passed by the U. S. Congress, and Cuba was required to include it within her own constitution. This gave the United States authority to intervene in Cuban affairs in order to maintain law and order. The U. S. also obtained Guantanamo Bay as a naval base in Cuba.