Activity in this theater in 1861 was dominated largely by the dispute over the status of the border state of Missouri. The Missouri State Guard, allied with the Confederacy, won important victories at the Battle of Wilson's Creek and the First Battle of Lexington. However, they were driven back at the First Battle of Springfield. A Union army under Samuel Ryan Curtis defeated the Confederate forces at the Battle of Pea Ridge in northwest Arkansas in March 1862, solidifying Union control over most of Missouri. The areas of Missouri, Kansas, and the Indian Territory (modern-day Oklahoma) were marked by extensive guerrilla activity throughout the rest of the war, the most well-known incident being the infamous Lawrence massacre in the Unionist town of Lawrence, Kansas of August 1863.