Complex sentence: It was left to Dillon to fight a last gallant but unsuccessful campaign in the December general election of 1918 which after a failure to reach a pact with Sinn Féin swept his party, but certainly not its constitutional democratic tradition, into oblivion.
Split into simpler sentences: It was left to Dillon to fight a last gallant but unsuccessful campaign in the general election of December 1918. After a failure to reach a pact with Sinn Féin, his party, but certainly not its constitutional democratic tradition, was swept into oblivion.