Republican war

It is remarkable that in so many great wars it has been the defeated who have won. The people who were left worst at the end of the war were generally the people who were left best at the end of the whole business. For instance, the Crusades ended in the defeated of Christians. But they did not end in the decline of the Christians; they ended in the decline of the Saracens. That huge prophetic wave of Muslim power which had hung in the very heavens above the towns of Christendom, that wave was broken, and never came on again. The Crusaders had saved Paris in the act of losing Jerusalem. The same applies to that epic of Republican war in the eighteenth century to which we Liberals owe our political creed. The French Revolution ended in defeat: the kings came back across a carpet of the dead at Waterloo. The Revolution had lost its last battle; but it had gained its first object. It had cut a chasm. The world has never been the same since. No one after that has ever been able to treat the poor merely as a pavement.



by G.K. Chesterton: The Giant



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Hi,



The underlined, "epic of Republican war"...



What is the republican war? I tried to google but could not get an answer.



And why "epic" is used here?