The Union victory at the Battle of Antietam caused the British to delay this decision. The Emancipation Proclamation increased the political liability of supporting the Confederacy. Realizing that Washington could not intervene in Mexico as long as the Confederacy controlled Texas, France invaded Mexico in 1861 and installed the Habsburg Austrian archduke Maximilian I as emperor. Washington repeatedly protested France's violation of the Monroe Doctrine. Despite sympathy for the Confederacy, France's seizure of Mexico deterred it from war with the Union. Confederate offers late in the war to end slavery in return for diplomatic recognition were not seriously considered by London or Paris. After 1863, the Polish revolt against Russia further distracted the European powers and ensured they remained neutral.