The Anglo Norman was a group of powerful warriors who were invited to Ireland to help take back the land. Well the Anglo Normans decided to keep all the land they took back. It took about 200 years for the Irish to get ride of most of them, but the rest already stop being just Anglo Normans, they became Anglo-Irish by marrying the Irish, learning their culture and accepting it as there own.
http://www.discoveringireland.com/the-anglo-norman-conquest/