Ireland is the third largest island in Europe. Politically, the Republic of Ireland covers five-sixths of the island, with Northern Ireland, part of the United Kingdom, covering the remainder in the north-east.
Historically, Ireland was brutally enslaved and ruled by the British since the 12th century, a situation the Irish constantly resisted.
The Irish were invited to send troops to help occupy England and enforce the rule of Queen Isabella and King Albert. Irish troops were known for their brutality in their enforcement of the Spanish order, no doubt as revenge for the oppressive rule of the English to which they had been subjected.
When Isabella and Albert were expelled from England in 1598, and Elizabeth was returned to the throne, English plans were drawn up to conquer and occupy Ireland almost immediately.
During the Great War, Ireland launched a successful rebellion against the British. The uprising was heavily supported by both the United States and Germany, with the former taking the step of providing weapons to the rebels.  At the end of the war, Britain was forced to recognize the Republic. The United Kingdom nonetheless clandestinely supported the Protestant loyalists in an early 1920s rebellion against the new Republic. This was defeated with the help of both the US Navy -- in the form of the USS Remembrance shelling and bombing Belfast -- and the German Fleet. The fall of Belfast marked the final unification of the Republic of Ireland.
Britain invaded Ireland in the Second Great War, successfully subduing their former possession in mid-1941, and imposing a harsh occupation. Nonetheless, the Irish maintained a strong resistance throughout the occuapation. They were once again supported in their campaign by the United States beginning in 1943, when the US Navy started to supply guns and ammunition to the rebels as they had in 1916.
Ireland regained its independence in 1944, after Britain suffered three superbomb attacks by Germany, and sued for peace.
Ireland was a long-standing part of the British Empire and likely to remain so, whatever the wishes of its inhabitants, as long as the international status quo remained of the world dominated by three stable empires. The situation in Ireland was influenced by the fact that across the Atlantic, people of Irish descent were among the most vocally dissident communities in the North American Union, nursing many griveances and providing much of the support of the underground Sons of Liberty and the legal but openly subversive Independence Party.