Complex sentence: In the United States, they were restricted to land assigned in the Fort Laramie Treaty of 1851 and were later given a distinct reservation in the Sweetgrass Hills Treaty of 1887.
Split into simpler sentences: In the United States, they were restricted to land assigned in the Fort Laramie Treaty of 1851. Nearly three decades later, they were given a distinct reservation in the Sweetgrass Hills Treaty of 1887.