Discuss how the Irish Civil War affected Irish Nationhood (i.e., leading the periods of division).

The respective sides in the Irish Civil War had different understandings of what constituted the Irish nation. These differences emerged from a split over the Anglo-Irish Treaty of 1921. The treaty, negotiated with the British, partitioned the island of Ireland in two. In the north, six of Ulster's counties—those with a Protestant majority—became Northern Ireland and remained a part of the United Kingdom. The rest of the country became the Irish Free State with its capital in Dublin, Ireland's largest city. Although the Irish Free State was now an independent country, it was still required to accept King George V of England as its head of state. Ireland wouldn't become a republic until 1948.
Most Irish people supported the Anglo-Irish Treaty, albeit with reservations. Although they would've preferred all thirty-two counties of Ireland to become a unified independent state, they figured that this was probably the best deal that they were ever likely to get from the British. They were reluctantly prepared to accept a restricted view of the Irish nation, one that excluded not just Protestants in the north, but also the minority Catholic population there.
Opponents of the treaty regarded it as nothing more than a sellout. The Irish had been engaged in a brutal armed struggle against the British, and it now seemed that that bitter, destructive conflict had all been for nothing. One of the leaders of that struggle was none other than Michael Collins, who played a lead role in negotiating the Anglo-Irish Treaty with the British. Anti-treaty forces regarded him as a traitor who'd betrayed his country. As far as they were concerned, not much had really changed. The British were still interfering in Irish affairs by retaining the six counties of Northern Ireland. Those hostile to the treaty also drew attention to the plight of the Catholic minority in Northern Ireland, who were subject to widespread discrimination in relation to housing and employment.