Complex sentence: In 1792, they were joined by 1200 Black Loyalists from Nova Scotia, African Americans and their descendants; some adults had left rebel owners and fought for the British in the revolutionary War.
Split into simpler sentences: In 1792, they were joined by 1200 Black Loyalists from Nova Scotia; these were African Americans and their descendants. Many of the adults had left rebel owners and fought for the British in the Revolutionary War.