The Plantation of Ulster
Ulster was dominated by Gaelic Irish clans, The O' Neills of Tyron and the O' Donnels of Donegal.
Queen Elizabeth, I hoped to control Ulster by giving Hugh O' Neill the title of ' Earl of Tyrone' as he had been accepting of the English rule and had been loyal to her. However, when the English sheriffs tried to enforce Protestantism, and English laws The O' Neills and The O' Donnels rebelled and asked the Catholic King Philip II of Spain for help as the Spanish were enemies of the English and had a powerful defense force.
King Philip did not send them any troops but did give them advice and the Gaelic Irish rebelled and fought agaianst the English rule leading to the Nine Years War between the Irish and the English. This inspired the Spanish King and he sent 4000 soldiers to support the Irish.
The ships landed in Kinsale Cork in 1601 but were captured by the English, O' Neill and O' Donnel tried to help but they were also defeated. Them and other cheifs fled for Spain in 1607 and this left Ulster very defenceless and the English gained more power over them and in 1609 King James I finally succeded in in overcoming Ulster and completely put them under English rule.