In August 1851, 40 Americans who took part in Narciso López's filibustering expedition in Cuba, including William L. Crittenden, were executed by Spanish authorities in Havana. In 1854, a secret proposal known as the Ostend Manifesto was devised by U.S. diplomats, interested in adding a slave state to the Union. The Manifesto proposed buying Cuba from Spain for $130 million. If Spain were to reject the offer, the Manifesto implied that, in the name of Manifest Destiny, war would be necessary. When the plans became public, because of one author's vocal enthusiasm for the plan, the manifesto caused a scandal, and was rejected, in part because of objections from anti-slavery campaigners.