Complex sentence: In 1901, Crosby was promoted to captain and assigned to the 14th Cavalry Regiment, with which he served at Fort Riley (Kansas), Fort Huachuca (Arizona), the Philippines, Fort Walla Walla (Washington), and Boise Barracks (Idaho).
Split into simpler sentences: In 1901, Crosby was promoted to captain and assigned to the 14th Cavalry Regiment. He served at Fort Riley (Kansas), Fort Huachuca (Arizona), the Philippines, Fort Walla Walla (Washington), and Boise Barracks (Idaho).