Since the Monroe Doctrine, the United States gained a major influence on most Caribbean nations. In the early part of the 20th century, this influence was extended by participation in the Banana Wars. Victory in the Spanish–American War and the signing of the Platt Amendment in 1901 ensured that the United States would have the right to interfere in Cuban political and economic affairs, militarily if necessary. With the Treaty of Paris, Spain ceded control of Cuba and Puerto Rico to the United States. Thereafter, the United States conducted military interventions in Cuba, Haiti, and the Dominican Republic. The series of conflicts ended with the withdrawal of troops from Haiti in 1934 under President Franklin D. Roosevelt.