Confederate forces under Earl Van Dorn attempted to take the war into the Border States in 1862. On March 7, 1862, those forces were met by Union soldiers led by Brig. General Samuel Ryan Curtis in a series of encounters on Pea Ridge in the hills of extreme northwest Arkansas, which continued the next day. Union forces under Curtis had driven Confederate troops out of Arkansas and into Indian Territory (later Oklahoma). He was headquarters at Fayetteville when he learned that the Confederate general Van Dorn was bringing a major force against him. He first strengthened his front, but Van Horn swung his army to the left and came up against Curtis' rear, severing his communications and denying him reinforcements. Curtis then reversed himself and faced Van Horn, whose forces attacked on the morning of the 7th. The Confederate strength was around 14,000 and Union forces numbered around 10,500. Both sides had some 50 cannons. At first, the Confederates seemed to carry all before them, but Union resistance, especially in the fighting at Elkhorn Tavern, turned the tide. Confederate officers James McQueen McIntosh and Benjamin McCulloch were both mortally wounded and their troops retreated. The Union defense at Pea Ridge was responsible for keeping the war from spreading into Missouri. The Confederates would not make another effort in this region until 1864.