Federal troops left Arizona early in 1861 to reinforce operations in the east, the territory had been left open to Apache attack. Most notably, Mangas Coloradas and Cochise led a series of raids on white civilians that left dozens dead and spread fear and terror across the territory. The Apache appeared to show equal hostility to both Union and Confederate forces, and both armies attempted to control them; the resulting engagements are often considered part of both the Civil War and the American Indian Wars. The remaining Union troops in the New Mexico Territory were concentrated in forts along and near the Rio Grande; the commander of the Union Department of New Mexico, Colonel Edward R.S. Canby, started raising regiments of New Mexico volunteers and militia to replace the regular army units which had been ordered east.