Around 1750, the British mainland American colonies had a population of approximately 1.5 million. In addition to settlers from Great Britain, a steady stream of German immigrants began to arrive in the late 1600s and reached its peak between 1749 and 1754, when more than 5,000 Germans arrived annually. Each year 3,500 black captives arrived from Africa or the Caribbean. Nearly 1 in 5 Americans, or 300,000 people, were enslaved. Poverty in Northern Ireland forced a massive flight of Scots-Irish to the colonies.