What role did migration. play in the middle of the colonies

answer:

Middle Colonies and the Western Frontier Unlike New England, the mid-Atlantic region gained much of its population from new immigration. By 1750, the combined populations of New York, New Jersey, and Pennsylvania had reached nearly 300,000 people after an influx of German, Swiss, and Irish immigrants. they earned money and became more popular

Explanation:

After Mexican debts were paid, all countries but France left.

France ignored the Monroe Doctrine and Napoleon III overthrew the Republic of Mexico.

Took advantage of the Civil War.