The Gaelic League was from the start strictly non-political, but in 1915, a proposal was put forward to abandon that policy and become a semi-political organisation. MacNeill strongly supported that and rallied to his side a majority of delegates at the 1915
Oireachtas na Gaeilge. Douglas Hyde, a non-political Protestant, who had co-founded the League and been its president for 22 years, resigned immediately afterwards. Through the Gaelic League, MacNeill met members of
Sinn Féin, the
Irish Republican Brotherhood (IRB), and other nationalists and republicans. One such colleague,
The O'Rahilly, ran the league's newspaper
An Claidheamh Soluis, and in October 1913 they asked MacNeill to write an editorial for it on a subject broader than
Irish language issues. MacNeill submitted a piece called "The North Began", encouraging the formation of a nationalist volunteer force committed to
Irish Home Rule, much as the
unionists had done earlier that year with the
Ulster Volunteers to thwart Home Rule in Ireland. In July 1915 MacNeill commented on the threat that the unarmed nationalists in Ulster might face: "...a demented...English driven Orange Army would be let loose upon the helpless Catholic people of Ulster, who would be driven out of the province or massacred where they stood."
Bulmer Hobson, a member of the IRB, approached MacNeill about bringing the idea to fruition, and, through a series of meetings, MacNeill became chair of the council that formed the
Irish Volunteers, later becoming its chief of staff. Unlike the IRB, MacNeill was opposed to the idea of an armed rebellion, except in resisting any suppression of the Volunteers, seeing little hope of success in open battle against the
British army. The Irish Volunteers had been infiltrated by the Irish Republican Brotherhood, which planned on using the organisation to stage an armed rebellion, to separate Ireland from the
United Kingdom and establishing an Irish Republic. The entry of the UK into the
First World War was, in their view, a perfect opportunity to do that. With the cooperation of
James Connolly and the
Irish Citizen Army, a secret council of IRB officials planned a
general rising at Easter 1916. On the Wednesday before Easter, they presented MacNeill with a letter, allegedly stolen from high-ranking British staff in
Dublin Castle, indicating that the British were going to arrest him and all the other nationalist leaders. Unbeknownst to MacNeill, the letter—called the Castle Document—was a forgery. When MacNeill learned about the IRB's plans, and when he was informed that
Roger Casement was about to land in
County Kerry with a shipment of German arms, he was reluctantly persuaded to go along with them, believing British action was now imminent and that mobilization of the Irish Volunteers would be justified as a defensive act. However, after learning that the German arms shipment had been intercepted and Casement arrested, and having confronted
Patrick Pearse, who refused to relent, MacNeill countermanded the order for the Rising by sending written messages to leaders around the country, and placing a notice in the
Sunday Independent cancelling the planned "manoeuvres". That greatly reduced the number of volunteers who reported for duty on the day of the Easter Rising. Pearse, Connolly and the others agreed that the uprising would go ahead anyway, but it began one day later than originally intended to ensure that the authorities were taken by surprise. Beginning on Easter Monday, 24 April 1916, the Rising lasted less than a week. After the surrender of the rebels, MacNeill was arrested although he had taken no part in the insurrection. The rebel leader
Tom Clarke, according to his wife Kathleen, warned her on the day before his execution, "I want you to see to it that our people know of his treachery to us. He must never be allowed back into the National life of this country, for so sure as he is, so sure will he act treacherously in a crisis. He is a weak man, but I know every effort will be made to whitewash him." ==Political life==