Complex sentence: If he wished to make war, let him look to Outremer, and to this end, Gregory endorsed the sale to Charles of the claims of Maria of Antioch on the Kingdom of Jerusalem, which had been rejected by the "Haute Cour" there.
Split into simpler sentences: If he wished to make war, let him look to Outremer. To this end, Gregory endorsed the sale to Charles of the claims of Maria of Antioch on the Kingdom of Jerusalem, which had been rejected by the "Haute Cour" there.