Fetterman's Trap, also known as the Fetterman Massacre, occurred during Red Cloud's War. It was an attack by a group of Native Americans, on US soldiers led by Captain Fetterman.

The soldiers were killed on 21st December, 1866.

A party of woodcutters was attacked, near Fort Phil Kearny, by a party of Sioux. As they had anticipated, a detachment of soldiers left the fort to protect the woodcutters. Many more Native Americans ambushed them and killed 81 soldiers, before blocking the route to the fort, rendering it unusable.

The Second Fort Laramie Treaty was negotiated, which brought peace to the region for eight years.