Tecumseh's War or Tecumseh's Rebellion was a conflict between the United States and Tecumseh's Confederacy, led by the Shawnee leader Tecumseh in the Indiana Territory. Although the war is often considered to have climaxed with William Henry Harrison's victory at the Battle of Tippecanoe in 1811, Tecumseh's War essentially continued into the War of 1812 and is frequently considered a part of that larger struggle. The war lasted for two more years, until 1813, when Tecumseh and his second-in-command, Roundhead, died fighting Harrison's Army of the Northwest at the Battle of the Thames in Upper Canada, near present-day Chatham, Ontario, and his confederacy disintegrated. Tecumseh's War is viewed by some academic historians as the final conflict of a longer-term military struggle for control of the Great Lakes region of North America, encompassing a number of wars over several generations, referred to as the Sixty Years' War.

Tecumseh's confederacy was a confederation of indigenous peoples in the Great Lakes region of North America that began to form in the early 19th century around the teaching of Tenskwatawa, called The Prophet by his followers. The confederation grew over several years and came to include several thousand warriors. Shawnee leader Tecumseh, the brother of The Prophet, developed into the leader of the group as early as 1808. Together, they worked to unite the various tribes against the European settlers who had been crossing the Appalachian Mountains and settling on their land.