The Irish in the First World War

Diarmaid Ferriter explains here:

"With the outbreak of the Great War, Redmond appealed to individual Irish Volunteers to join the war effort as a moral imperative. MacNeill accused him of mental and moral corruption and insisted British parties were conspiring to stop Home Rule, a defeat that only the Irish Volunteers could prevent. 

A split ensued, with Redmond supported by a majority of Volunteers, by a ratio of 15 to one, now termed the National Volunteers, while MacNeill retained command of the minority, keeping the original title."