The French project for an expedition to Ireland hung on the junction of the Dutch fleet with that of Brest, and the command of the Channel which this junction would have given them. Such a command became impossible after the defeat of Camperdown. But the disappointment of their hopes of foreign aid only drove the adherents of revolt in Ireland to a rising of despair. The union of the national party, which had lasted to some extent from the American war, was now broken up. The Protestants of Ulster still looked for aid to France. The Catholics, on the other hand, were alienated from the French by their attack on religion and the priesthood; and the failure of the French expedition, while it damped the hopes of the Ulstermen, gave force to the demands of the Catholic party for a purely national rising. So fierce was this demand that the leaders of the United Irishmen were forced to fix on the spring of 1798 for the outbreak of an insurrection, in which Lord Edward Fitzgerald, who had some small military experience, was to take the command. But while yielding on this point to the Catholic section of their party they conciliated the Protestants by renewed appeals for aid to the Directory. In spite of its previous failures France again promised help; and a division was prepared during the winter for service in Ireland. But the passion of the nation was too intense to wait for its arrival. The government too acted with a prompt decision in face of the danger, and an arrest of Lord Edward Fitzgerald with three of their chief leaders in February 1798 broke the plans of the insurgents. On the 23rd of May, however, the day fixed for the opening of the revolt, the Catholic peasantry of the south rose in arms. Elsewhere their disorderly gatherings were easily dispersed by the yeomanry; but Wexford surrendered to 14,000 insurgents who marched on it, headed by a village priest, and the town at once became the centre of a formidable revolt.
Fortunately for the English rule the old religious hatred which had so often wrecked the hopes of Ireland broke out in the instant of this triumph. The Protestant inhabitants of Wexford were driven into the river or flung into prison. Another body of insurgents, frenzied by the cruelties of the royal troops, massacred a hundred Protestants in cool blood. The atrocities of the soldiers and the yeomanry were avenged with a fiendish ruthlessness. Loyalists were lashed and tortured in their turn, and every soldier taken was butchered without mercy. The result of these outrages was fatal to the insurrection. The Ulster Protestants, who formed the strength of the United Irishmen, stood sullenly aloof from rebels who murdered Protestants. The Catholic gentry threw themselves on the side of the government against a rising which threatened the country with massacre and anarchy. Few in fact had joined the insurgents in Wexford when Lord Lake appeared before their camp upon Vinegar Hill with a strong force of English troops on the 21st of May. The camp was stormed, and with the dispersion of its defenders the revolt came suddenly to an end. But its suppression came only just in time to prevent greater disasters; for a few weeks after the close of the rebellion the long-expected aid arrived from France. The news of the outbreak had forced the armament which was being equipped in the French ports to put to sea with forces utterly inadequate to the task it had set itself, but fresh aid was promised to follow, and the nine hundred soldiers who landed in August under General Humbert on the coast of Mayo showed by their first successes how formidable a centre they would have given to the revolt had the revolt held its ground. But in the two months which had passed since Vinegar Hill all trace of resistance to the English rule had been trodden out in blood, and Humbert found himself alone in a country exhausted and panic-stricken. He marched however boldly on Castlebar, broke a force of yeomanry and volunteers three times his number, and only surrendered when Lord Cornwallis, who had succeeded to the Lord-Lieutenancy, faced him with thirty thousand men.