For almost a year at the start of the Civil War, Missouri had teetered, but the the unexpected slaughter on the battlefields of 1862 had its most devastating effects of Confederate aspirations across the country. The South saw the first clear defeats of the Confederate armies in the East in 1863 and the loss of the Misssissippi river to the Union, severing the Transmississippi Confederacy. The next year brought bloody Union successes in Virginia and Georgia that brought the secessionist hopes nearly to an end.
Gen. Sterling Price had a plan. Transfers had badly depleted the Union forces west of the Mississippi while the Union held on the river denied the Confederates an opportunity to make such transfers. In the Spring, Union offensives on the Red River in Louisiana and in Arkansas failed. Price saw the opportunity to reenter Missouri, bringing the battlelines of late 1864 back to where they were first drawn in 1861. The capture of St. Louis would again close the Mississippi and the seizure of the capital at Jefferson City would permit the installation of the state's secessionist government-in-exile. If it happened before the November elections, such successes would severely damage the reelection bid of President Abraham Lincoln.
Slipping through the porous Union line along the Arkansas river, Price assembled a ragged force of 12,000 in northeastern Arkansas. His Confederate Army of Missouri began to enter the Federal Department of Missouri on Friday, September 16.
Gen. William S. Rosecrans had fought and defeated Price two years earlier at Iuka and Corinth in Mississippi. By late 1864, he believed the Confederacy largely played out, and steadfastly refused to acknowledge the presence, scale or command of this invading force. He did not call for a general mobilization of the militia until the closing days of September. Then, with his few volunteer regiments concentrated at St. Louis, Jefferson City and Rolla, Rosecrans left the defense of the state largely in the hands of that militia.
Meanwhile, Gen. Samuel R. Curtis who had fought and defeated Price's army two and a half years before at Pea Ridge mobilized the Federal forces in Kansas. By late 1864, he believed the Confederacy largely played out, and steadfastly refused to acknowledge the presence, scale or command of this invading force.