The early to mid 17th Century was not a good time for the Irish. It started with the Plantation of Ulster (which is the event at the root of the current Anglo-Irish question in Northern Ireland) in 1609 and ended with the English killing roughly half a million of them and James II and Oliver Cromwell selling 300,000 of them, of whom about 10% were political prisoners, into slavery in the West Indies. In the course of the decade(ish) between 1641 and 1652, the Irish population fell from just under a million and a half to 616,000.
By 1652, 70% (!) of the white population of Montserrat was Irish; through the entire decade of the 1650s, there were more Irish slaves living in the Americas than there were free citizens.
The first recorded instance of Irishmen being sold into slavery is 1612, when James II sold a group of them to a settlement on the Amazon. With the issue of a 1625 proclamation* that stated that Irish political prisoners (which considering the politics of the time, was all Irishmen) were to be banished overseas, the practice of selling the Irish into slavery became widespread.
In the 1650s, somewhere between 80,000 – 130,000 (depending on which source you read), Irish — many of whom were kidnapped — were sold into slavery in New England, Virginia, and the Caribbean. The reason for this? They were much cheaper than African slaves. African slaves cost between 50-60 pounds sterling; the Irish cost five. Turns out that the reason for this price difference is that the Africans weren’t tainted by Catholic dogma. Serio. As a result, they were treated a hell of a lot better than the Irish. For a while, realizing they could turn a sweet profit on it, slave owners bred Irish women (and, let’s be real, girls) and African men to create an entire generation of mixed-race slaves who brought more money than the Irish at market, but weren’t as expensive as the Africans. The practice was so widespread that in 1681 a law was passed outlawing “the mating of Irish women and African men for the purpose of producing slaves for sale,” not because it was immoral, but because it was cutting into the profits of the Royal African Company, which provided African slaves to the New World.
Part of the reason the number of Irish slaves was so high is because Cromwell continued the work the Plantation of Ulster started, issuing a decree that stated that all Irish must relocate west of the Shannon River into Connaught (the westernmost of the four Irish provinces) or County Clare (part of Muenster, but the county immediately south of Connaught).** By 1657, he had issued a law that gave the Irish six months to abandon their lands east of the Shannon or be held as traitors and banished to America, never to return lest they “suffer the pains of death as felons by virtue of this act, without benefit of Clergy.”***
While the flow of Irish into the West Indies (and America) ebbed after 1660 (because the English had already sent off nearly everyone they could), there was still a continuous trade in Irish slaves throughout the rest of the 17th and into the 18th century. After the 1798 Irish rebellion, thousands were sent to be sold as slaves in the United States and Australia.
Transportation of Irish slaves finally ended in 1839 when Britain decided to end their involvement in the slave trade.
Interesting side note: there was a brief Irish uprising in the Barbados in 1649, which Cromwell quickly crushed. He had the perpetrators drawn and quartered and mounted their heads on pikes.
*I can’t find whatever proclamation these sources talk about, but there are a slew of sources cited (including Abbott Smith’s Colonists in Bondage: White Servitude and Convict Labour in America, 1607-1776), so at some point, someone actually read it.
**If you’ve ever been to Co. Clare, you understand why this is a bit of a problem. It’s super cool terrain, but, being mostly rock, not so good for farming.
***I also can’t find this law, but it’s also cited in a ton of places (including Rhetta Akamatsu’s The Irish Slaves: Slavery , Indenture, and Contract Labor Among Irish Immigrants), so ostensibly someone read that one too.