The conquest of Ireland by England began in the 12th century.

An excerpt from the article 39 facts about Ireland

Most Irish rulers paid tribute to Henry II, but this conquest was partial, the English never managed to take over the entire island. There was increasing resistance from native Irish leaders to English authority. Some of the newcomers were Celticized, although the English tried to maintain the independence of the colonists. Around 1400, the area of the English colony in Ireland was limited to a small area around Dublin (the so-called Stockade).