Phillip is pretty wrong and obviously biased, both nationalists and unionists did not officially exist at the the time, those terms came about to describe those in Northern Ireland after its creation, the terms used would have been Republicans/rebels and Loyalists, both denominations fought in WW1, and were not discriminated against because of religious or political belief but purely because they were Irish commoner, who were looked down upon by the English gentry as well as most of the English population as they had always been in servitude to both English and even Irish landlords, much like the Scottish and Welsh were. Many thousands of Irish died during WW1 and the irish suffered the heaviest losses at the battle of the Somme, there is even a huge WW1 and 2 memorial in Dublin which was visited by Queen Elizabeth on her recent and first visit ( by any English monarch ) to the Republic of Ireland. Conscription was never introduced in Ireland and the partition was never completed until 23 May 1921, when the free state was created along with the creation of a Northern Ireland. Be careful when asking about Irish history as ignorance and bigotry have prevented most people from actually Being unbiased!