On September 4, 1861, Confederate General Leonidas Polk, outraged by Union intrusions in the state, invaded Columbus, Kentucky. As a result of the Confederate invasion, Union General Ulysses S. Grant entered Paducah, Kentucky. Jefferson Davis allowed Confederate troops to stay in Kentucky. General Albert Sidney Johnston, commander of all Confederate forces in the West, sent General Simon Bolivar Buckner of Kentucky to invade Bowling Green, Kentucky. Union forces in Kentucky saw Buckner's move toward Bowling Green as the beginning of a massive attack on Louisville. With twenty thousand troops, Johnston established a defensive line stretching from Columbus in western Kentucky to the Cumberland Gap, controlled by Confederate General Felix Zollicoffer.