Answer: D
Explanation: Buffalo Soldiers were African American troops who served in the western frontier of the United States from the late 1860s to the early 1900s. They were initially assigned to the segregated regiments of the U.S. Army, which included the 9th and 10th Cavalry Regiments and the 24th and 25th Infantry Regiments.
Their primary role was to provide military protection to settlers, stagecoaches, wagon trains, and other groups as they migrated and settled in the western regions of the United States. They were tasked with maintaining law and order, guarding against Native American resistance, and defending American interests during the westward expansion.
The Buffalo Soldiers played a significant role in maintaining peace, establishing forts, building infrastructure, and providing security during a challenging and often dangerous period in American history.