The military occupation of the Confederacy by the United States of America was a military occupation and guerrilla conflict that lasted between March of 1916 and December of 1921. The occupation was agreed upon as part of the terms of the Treaty of Lexington signed in 1916, and allowed for the stationing of American soldiers in the Confederate states of Arizona, New Mexico, Oklahoma, Kentucky, Tennessee and Virginia, as well as smaller deployments in strategic port cities such as New Orleans, Galveston, Norfolk and Savannah. The occupation existed ostensibly to protect the American border and ensure the transfer of shipping rights on the Mississippi River and through the Chesapeake Bay, major causes for the war between the USA and CSA.
The occupation was deeply controversial in the South, in particular amongst poor whites who had overwhelmingly fought in the Confederate Army and felt betrayed by politicians who agreed to "Yankee boots on Southern soil." The loss to the Union in the war had come as a great shock to the military and political establishment as well, as the Confederacy had never lost a war prior and Presidents Woodrow Wilson and William G. McAdoo had been convinced of the nation's invincibility in conflict and the lack of will within the Union to fight to the finish.
The Illegal Occupation, as it came to be known, quickly led to the formation of guerrilla units, most notably the Sons of the South, the Last Defense Regiment, and the secretive Ku Klux Klan. While the Union occupation existed mostly in the West and Upper South as well as a handful of cities, the majority of recruits for these guerrilla units came from Alabama, Mississippi, Georgia and South Carolina. The fighting became so severe in 1918 that President Theodore Roosevelt of the United States deployed an additional two divisions to Kentucky and Virginia, further enraging the Confederate populace.
The long-term effects of the Illegal Occupation were more widespread. In addition to deepening resentments against the Union, nearly five million blacks fled the South, crippling the agrarian economy and sending the Confederacy into a deep depression that lasted into the 1940s. Confederate Nationalism rose dramatically, and there was a backlash against what was perceived as an inept government in Richmond. The National Democratic Party lost control of both houses of Congress in the 1919 elections and lost the Presidency in 1921 as the Southern Front candidate, Senator John C.W. Beckham of Kentucky, defeated Senator Joseph W. Bailey of Texas. The National Democrats largely vanished as a viable federal party shortly thereafter.
In the United States, the Democrats retook Congress in 1918 largely based on their opposition to foreign entanglements and the Socialists won the three-way Presidential election in 1920 on the strength of Robert La Follette's campaign against the occupation. Throughout the summer of 1921, the La Follette administration negotiated with the McAdoo administration to withdraw soldiers by the end of the year in return for permanent and inviolable shipping rights through the Hampton Roads and Mississippi River. On December 31, the last Union troops were removed from Confederate soil, and the bands played "The Star-Spangled Banner" and "Dixie" as American soldiers crossed the Potomac back into Washington, D.C.