About 146,000 Irish were fighting in the Great War

The outbreak of the first World War seemed at first to put Ireland's internal troubles in the shade. The Home Rule Bill, which was to create an all-Ireland parliament, was suspended until the end of hostilities. The British authorities believed that the war removed the threat of trouble in Ireland. Potential conflict between Ulster Volunteers pledged to fight against Home Rule and the National Volunteers, who had armed themselves to fight for it, seemed to have been defused.

With Ulster Volunteers recruited for the Ulster Division, the Irish Parliamentary Party leader John Redmond matched the offer, and urged members of the Volunteers to serve in the British army "wherever the firing line extends". However, some nationalists wanted to act on the slogan "England's difficulty is Ireland's opportunity". A split in the National Volunteers over the war left a smaller faction of Irish Volunteers, which was easier for the militants in the Irish Republican Brotherhood to control.

Their support for the war gradually eroded the authority of John Redmond and his Irish Parliamentary Party as the initial flush of popular enthusiasm turned to wariness about the possibility of forced conscription. The British government feared that disarming the Irish Volunteers and Irish Citizen Army in this unsettled atmosphere might create a backlash that would affect army recruitment.

In 1916 some 146,000 Irish were fighting in the Great War. On the Thursday, the 16th (Irish) Division of the British Army lost over 550 men in a single gas attack at Hulluch, Belgium. The crowds of angry women who gathered throughout Easter Week to denounce the rebels were mostly the wives of these soldiers, or widows of those killed.

While many nationalists were among those fighting in the British Army, there was little support for the Easter Rising, and many felt betrayed by it. As news came through to the Front, German soldiers taunted Irish with the message that "English guns are firing at your wives and children".

With the change in public attitude following the executions of its leaders, dissatisfaction with the war grew in Ireland. The Nationalist MP and poet, Thomas Kettle, who was killed in the Great War, had prophesised that the Easter rebels "will go down to history as heroes and martyrs, and I will go down - if I go down at all - as a bloody British officer."

In all, between 25,000-35,000 Irish-born soldiers died in the first World War. However, many of the soldiers who returned to an increasingly nationalist Ireland received a grudging and sometimes hostile welcome.