Complex sentence: Starting at around the same time as the War of 1812, the Shawnee entered war with the United States over land rights under the famous Tecumseh, in which they were steadily pushed west, down the Ohio, then the Mississippi, into the Ozarks.
Split into simpler sentences: Starting at around the same time as the War of 1812, the Shawnee entered war with the United States over land rights, under the famous Tecumseh. During this time, they were steadily pushed west, down the Ohio, then the Mississippi, into the Ozarks.