The annexation of Santo Domingo was an attempted treaty during the later Reconstruction era, initiated by United States President Ulysses S. Grant in 1869, to annex "The Spanish province of Santo Domingo" as a United States territory, with the promise of eventual statehood. President Grant feared some European power would take the island country in violation of the Monroe Doctrine. He privately thought annexation would be a safety valve for African Americans who were suffering persecution in the U.S., but he did not include this in his official messages. Grant speculated that the acquisition of Santo Domingo would help bring about the end of slavery in Cuba and elsewhere.

Ulysses S. Grant was an American military officer, politician, and the 18th president of the United States from 1869 to 1877. As commanding general, Grant led the Union Army to victory in the American Civil War in 1865 and briefly served as U.S. secretary of war. An effective civil rights executive, Grant signed a bill to create the Justice Department and worked with Radical Republicans to protect African Americans during Reconstruction.