Pierre Soulé was a French-American slaveholder, attorney, politician, and diplomat in the mid-19th century. Serving as a U.S. senator from Louisiana from 1849 to 1853, he was nominated that year as U.S. Minister to Spain, a post that he held until 1855.

The Ostend Manifesto, also known as the Ostend Circular, was a document written in 1854 that described the rationale for the United States to purchase Cuba from Spain while implying that the U.S. should declare war if Spain refused. Cuba's annexation had long been a goal of U.S. slaveholding expansionists. At the national level, American leaders had been satisfied to have the island remain in weak Spanish hands so long as it did not pass to a stronger power such as Britain or France. The Ostend Manifesto proposed a shift in foreign policy, justifying the use of force to seize Cuba in the name of national security. It resulted from debates over slavery in the United States, manifest destiny, and the Monroe Doctrine, as slaveholders sought new territory for the expansion of slavery.