Great Plains. Meanwhile, the Confederacy admits Kentucky, Sequoyah, and Cuba as new states, and negotiates the purchase of Sonora and Chihuahua from Mexico in 1881. Republican President James G. Blaine uses this as a casus belli to declare a renewed war, drawing Britain and France back into the conflict. The Union, despite its advantage in manpower and resources, lacks competent leadership, and struggles to take Confederate territory while also facing a revolt in Utah. The Louisville campaign devolves into trench warfare, while Britain and France shell U.S. ports and New Brunswick annexes northern Maine. The Union capitulates in early 1882, recognizing the Confederate acquisitions, while the Republicans are soon voted out of government. In the wake of the war's loss, Lincoln leads his loyal faction of the Republican Party into merging with the nascent Socialist Party of America, changing US politics as this becomes the second major party, supplanting the Republicans afterward. Over the rest of the decade, manumission of slaves is nominally implemented throughout the Confederacy—easing relations with Britain and France, which had both abolished slavery much earlier—although the black population continues to live in apartheid-like conditions. The U.S. secures an alliance with the new German Empire amid a national atmosphere of revanchism. Great War Upon the assassination of Archduke Franz Ferdinand, Britain, France, and Russia go to war with Germany and Austria-Hungary. Presidents Theodore Roosevelt and Woodrow Wilson order the U.S. and C.S. militaries to mobilize following their respective allies, and fighting soon breaks out. Industrialized warfare and the absence of European intervention favors the Union side, and much of the Confederate officer corps is made up of heirs of great 19th-century generals with no particular talent of their own. An invasion of Maryland and Pennsylvania overruns Washington, D.C. but is unable to take Baltimore, while the Union launches attacks on Sonora and Canada, along with the capture of the British Sandwich Islands. As winter falls, a stalemate settles in across trench lines in Kentucky, Pennsylvania, Virginia, Manitoba, Southern Ontario, and the St. Lawrence River. The U.S. faces another rebellion in Utah and the C.S. faces a black socialist revolt, which takes a year to subdue. In 1916 a new technical advance is introduced: the "barrel". George Armstrong Custer develops a doctrine for armored cavalry, but his tactics are not adopted and the first offensive is a failure. The U.S. successfully advances in Canada and defends Hawaii in