Complex sentence: The United States Colored Troops (USCT) were regiments in the United States Army composed of mainly African-American (colored) soldiers, although non-African Americans people of color such as Pacific Islanders, Asian Americans and Native Americans also fought under USCT regiments.
Split into simpler sentences: The United States Colored Troops (USCT) were regiments in the United States Army composed primarily of African-American (colored) soldiers. Other people of color who were not of African descent, such as Pacific Islanders, Asian Americans and Native Americans also fought under USCT regiments.