Background: Gaelic Ireland (Irish: Eire Ghaidhealach) was the Gaelic political and social order, and associated culture, that existed in Ireland from the prehistoric era until the early 17th century. Before the Norman invasion of 1169, Gaelic Ireland comprised the whole island. Thereafter, it comprised that part of the country not under foreign dominion at a given time. For most of its history, Gaelic Ireland was a "patchwork" hierarchy of territories ruled by a hierarchy of kings or chiefs, who were elected through tanistry.
Context: Ireland became Christianized between the 5th and 7th centuries. Pope Adrian IV, the only English pope, had already issued a Papal Bull in 1155 giving Henry II of England authority to invade Ireland as a means of curbing Irish refusal to recognize Roman law. Importantly, for later English monarchs, the Bull, Laudabiliter, maintained papal suzerainty over the island:  In 1166, after losing the protection of High King Muirchertach Mac Lochlainn, King Diarmait Mac Murchada of Leinster was forcibly exiled by a confederation of Irish forces under King Ruaidri mac Tairrdelbach Ua Conchobair. Fleeing first to Bristol and then to Normandy, Diarmait obtained permission from Henry II of England to use his subjects to regain his kingdom. By the following year, he had obtained these services and in 1169 the main body of Norman, Welsh and Flemish forces landed in Ireland and quickly retook Leinster and the cities of Waterford and Dublin on behalf of Diarmait. The leader of the Norman force, Richard de Clare, 2nd Earl of Pembroke, more commonly known as Strongbow, married Diarmait's daughter, Aoife, and was named tanaiste to the Kingdom of Leinster. This caused consternation to Henry II, who feared the establishment of a rival Norman state in Ireland. Accordingly, he resolved to visit Leinster to establish his authority.  Henry landed in 1171, proclaiming Waterford and Dublin as Royal Cities. Adrian's successor, Pope Alexander III, ratified the grant of Ireland to Henry in 1172. The 1175 Treaty of Windsor between Henry and Ruaidhri maintained Ruaidhri as High King of Ireland but codified Henry's control of Leinster, Meath and Waterford. However, with Diarmuid and Strongbow dead, Henry back in England, and Ruaidhri unable to curb his vassals, the high kingship rapidly lost control of the country. Henry, in 1185, awarded his younger son, John, the title Dominus Hiberniae, "Lord of Ireland". This kept the newly created title and the Kingdom of England personally and legally separate. However, when John unexpectedly succeeded his brother as King of England in 1199, the Lordship of Ireland fell back into personal union with the Kingdom of England.
Question: Were invasions common?
Answer: 

Background: Daniel Lee Dierdorf (born June 29, 1949) is a former American football offensive lineman and current sportscaster. A native of Canton, Ohio, Dierdorf played college football for the University of Michigan from 1968 to 1970 and was selected as a consensus first-team All-American in 1970 and a first-team All-Big Ten Conference player in 1969 and 1970. He was inducted into the University of Michigan Athletic Hall of Honor in 1996 and the College Football Hall of Fame in 2000. Dierdorf played professional football in National Football League (NFL) with the St. Louis Cardinals for 13 seasons from 1971 to 1983.
Context: From 1974 to 1976, Dierdorf started every game at right tackle for the Cardinals during a three-year span in which the team compiled records of 10-4, 11-3, and 10-4 under head coach Don Coryell. In 1977, Dierdorf sustained a broken jaw and missed two games to injury as the Cardinals fell to 7-7. In 1978, Dierdorf started all 16 games at right tackle for the Cardinals.  During his peak years from 1974 to 1978, Dierdorf was regarded as one of the best offensive lineman in the NFL. He was selected by the National Football League Players Association as the Offensive Lineman of the Year for three consecutive years from 1976 to 1978. The Cardinals' offensive line, led by Dierdorf, Conrad Dobler, and Tom Banks, led the NFL with the fewest sacks allowed for three years (and the National Football Conference for five years) in the mid-1970s. In 1975, the group set an NFL record, allowing only eight sacks in 14 games.  Dierdorf did not allow a sack during the entire 1976 and 1977 seasons. His streak ended in the first game of the 1978 season when Chicago Bears defensive end Tommy Hart tallied two sacks against Dierdorf. Dierdorf had not given up a sack since the 1975 NFC Divisional playoff game when Jack Youngblood sacked Jim Hart.  Dierdorf was selected to play in the Pro Bowl for five consecutive years from 1974 to 1978. Dierdorf also received first-team All-NFL honors as follows: in 1975 from the Pro Football Writers Association (PFWA); in 1976 from the Associated Press (AP), PFWA, Newspaper Enterprise Association (NEA), and Pro Football Weekly (PFW); in 1977 from AP, PFWA, NEA, and PFW; and in 1978 from AP, PFWA, NEA, PFW. He was named as the NFC choice for the NFLPA/Coca-Cola Offensive Lineman of the Year Award three straight years (1976-78) and was the Seagram's Seven Crowns of Sports Offensive Lineman of the Year in 1975. He also won the Forrest Gregg Award for NFL Offensive Lineman of the Year in 1975.
Question: Who did he play  for during this time?
Answer:
the Cardinals