Complex sentence: It was originally called the Tongue River Cantonment for the first year or so; then relocated a mile away and renamed Fort Keogh in honor of Captain Myles Keogh, who died at the Battle of the Little Bighorn.
Split into simpler sentences: It was originally called the Tongue River Cantonment for the first year or so. When relocated a mile away it was renamed Fort Keogh in honor of Captain Myles Keogh, who died at the Battle of the Little Bighorn.