In response to the French invasion and the elevation of Maximilian as Emperor of Mexico, Juárez sent General Plácido Vega y Daza to California to gather Mexican American sympathy for republican Mexico. Maximilian offered Juárez amnesty and later the post of prime minister, but Juárez refused to accept a government "imposed by foreigners," or a monarchy. The US government was sympathetic to Juárez, refusing to recognize Maximilian and opposing the French invasion as a violation of the Monroe Doctrine. Most of its attention was taken up by the American Civil War.