The Normans were Vikings who had settled in Normandy in the north of France. In 1066 the leader of the Normans, William, defeated the King of England, Harold, at the Battle of Hastings. William became King of England. One hundred years later, King Henry II, William's grandson, wanted to expand his kingdom by conquering Ireland. 

Henry got his chance to conquer Ireland when the King of Leinster, Dermot MacMurrough, was driven out of his kingdom. He went to England to seek help in regaining control over his land. King Henry gave him permission to recruit support from his subjects. 

Dermot MacMurrough met Strongbow, a Norman lord, and enlisted his help in regaining control over his land. MacMurrough promised Strongbow two things in return for his support - his daughter's hand in marriage and that Strongbow would inherit the Kingdom of Leinster upon MacMurrough's death. The Normans landed in Ireland in 1169. MacMurrough won back Leinster with the help of Strongbow and his army. Not long after this, MacMurrough died and Strongbow became King of Leinster. 

King Henry followed Strongbow to Ireland in 1172. He was afraid Strongbow would become too powerful and eventually become King of Ireland. Henry asserted his power and gave big pieces of land to other Norman lords. He had succeeded in conquering Ireland. English kings ruled Ireland for almost 800 years after that.