This became more brutal than the war of independence before it, with massacres and atrocities committed by both sides. The Boundary Commission that was set up as part of the Treaty to realign of the border between Northern Ireland and the Free State did not meet until 1924. The Chairman of the Commission, Feetham, was not inclined to make any big changes. The Free State drew up a minimum negotiating position that would gain Fermanagh, most of Tyrone and parts of Down and Armagh for the South. This left substantial unionist minorities in Donegal and Monaghan and nationalist majorities in Fermanagh and Tyrone all on the wrong side of the border.
Irish history is one of the topics that comes up again and again on soc.culture.irish .
Some regulars have devoted much of their own web pages to the subject.