On April 1, 1901, Emilio Aguinaldo volunteered to swear his allegiance to the United States, formally ending the First Republic and recognizing the sovereignty of the US over the Philippines. He signed an oath of allegiance to the United States, nine days after his capture, in return for his release from incarceration. Aguinaldo was captured by the Americans in his secret headquarters in Palanan, Isabela on March 23, 1901.