Original: However the slow pace of developments, contributed in part to the (wider) political difficulties of the British government of John Major and consequent reliance on Ulster Unionist Party votes in the House of Commons, led the IRA to end its ceasefire and resume the campaign.
Simplified: However the IRA ended its ceasefire because of the slow pace of developments, partly because British prime minister John Major needed the votes of the Ulster Unionist Party in the House of Commons.