Complex sentence: Kantakouzenos was far too ready to invoke the aid of foreigners in his European quarrels; and as he had no money to pay them, this gave them a ready pretext for seizing upon a European town.
Split into simpler sentences: Kantakouzenos was far too ready to invoke the aid of foreigners in his European quarrels. Since he had no money to pay them, this gave them a ready pretext for seizing upon a European town.