Complex sentence: The Mongols invaded Syria several times between 1281 and 1312, sometimes in attempts at joint operations with the Franks, but the considerable logistical difficulties involved meant that forces would arrive months apart, never able to coordinate activities in any meaningful way.
Split into simpler sentences: The Mongols invaded Syria several times between 1281 and 1312, sometimes in attempts at joint operations with the Franks. But the considerable logistical difficulties involved meant that their forces were never able to coordinate their simultaneous arrival, and thus could not cooperate in any meaningful way.