Complex sentence: Ireland initially scheduled a referendum for the autumn 2013 on a constitutional amendment required to ratify the agreement, was subsequently postponed to an unscheduled date after the 2014 European Parliament election.
Split into simpler sentences: Ireland initially scheduled a referendum for the autumn 2013 on a constitutional amendment required to ratify the agreement. However, the referendum was subsequently postponed to an unscheduled date after the 2014 European Parliament election.