The Anglo-Irish War

A militant group of nationalists (IRB) used this to their advantage in conjunction with WW1 to stage an uprising. The rebels seized on WW1 as an opportunity for rebellion, acting on the thought that "England's difficulty is Ireland's opportunity". Initially, the rebels were condemned by the majority Irish population, labelled as fools and traitors committing acts of treason whilst fellow Irishmen fell to the grounds on the battlefields of Europe. However, evidence does suggest, that many of the Irish felt a sense of pride that the rebels had enjoyed some measure of success by withstanding the might of the British army for a week. No other group in Ireland had achieved this feat before, indicating to some the possible viability of revolutionary nationalism. .
             Cause #2 British Response to the Easter Rising.
             The British response to the Easter Rising had a slow drip like effect on the Irish population, and wore away any resentment many members of the public may have previously held. It had the effect of converting the defeated and discredited rebels into martyrs and turned a failed revolt into a triumphant resurrection of Irish nationalism, effectively sowing the seeds of lasting rebellion in Ireland. While the actions of the rebels had resulted in Britain enjoying some popular measure of support for the first time in history as the popular force in Irish eyes, they had now ended up back where they began, the hated and resented occupying force. Irish Nationalist Party (INP) MP John Dillon urged and pleaded with the British parliament to end the executions, saying "You are washing out our whole lives work, in a sea of blood", as he felt that all the work his party had achieved through constitutional nationalism was being washed away by the 16 executions and the imposition of martial law. Not only were the 16 were now regarded as martyrs by the Irish, the arrests of thousands of innocent Irish under martial law fuelled anger and resentment.