The Navigation Acts, excluding Ireland from direct trade with the colonies, ruined Irish commerce, while Corporation Acts and Test Acts requiring conformity with the practices of the Church of England bore heavily on the Ulster Presbyterians.
It was largely by refugees from religious persecution that America in the beginning was colonized.

But religious persecution was only one of the influences which shaped the course and formed the character of the Ulster Scots.

In Ulster, whither they had originally been transplanted by James to found a loyal province in the midst of the King's enemies, they had done their work too well and had waxed too powerful for the comfort of later monarchs.

The first attacks upon them struck at their religion; but the subsequent legislative acts which successively ruined the woolen trade, barred nonconformists from public office, stifled Irish commerce, pronounced non-Episcopal marriages irregular, and instituted heavy taxation and high rentals for the land their fathers had made productive--these were blows dealt chiefly for the political and commercial ends of favored classes in England.
These attacks, aimed through his religious conscience at the sources of his livelihood, made the Ulster Scot perforce what he was--a zealot as a citizen and a zealot as a merchant no less than as a Presbyterian.
Thanks to his persecutors, he made a religion of everything he undertook and regarded his civil rights as divine rights.

Thus out of persecution emerged a type of man who was high-principled and narrow, strong and violent, as tenacious of his own rights as he was blind often to the rights of others, acquisitive yet self-sacrificing, but most of all fearless, confident of his own power, determined to have and to hold.
Twenty thousand Ulstermen, it is estimated, left Ireland for America in the first three decades of the eighteenth century.