Daniel O 'Connell led a subsequent campaign , for the repeal of the Act of Union , which failed . Later in the century , Charles Stewart Parnell and others campaigned for autonomy within the Union , or " Home Rule " . Unionists , especially those located in Ulster , was strongly opposed to Home Rule , which they thought would be dominated by Catholic interests . After several attempts to pass a Home Rule bill through parliament , it looked certain that one would finally pass in 1914 . To prevent this from happening , the Ulster Volunteers was formed in 1913 under the leadership of Edward Carson .