Despite achieving several early victories, Price was ultimately defeated at the Battle of Westport by Union forces under Major-General Samuel R. Curtis in late October. He suffered further reverses at the hands of Union cavalry under Major-General Alfred Pleasonton at the Battle of Mine Creek, Kansas, forcing him to retreat back into Arkansas. Price's Missouri Expedition proved to be the last significant Southern operation west of the Mississippi River. Its failure bolstered confidence in an ultimate Union victory in the war, thereby contributing to President Abraham Lincoln's re-election. It also cemented Federal control over the hotly contested border state of Missouri.