Complex sentence: The results of betrayal were that the Georgian army's 1/4 was completely annihilated, leaving country defenseless against Mongol invasions of Georgia, capture of Dvin and bringing about the end of Georgia's medieval heyday.
Split into simpler sentences: The results of betrayal were that the Georgian army's 1/4 was completely annihilated, leaving country poorly steeled against an upcoming Mongol invasion. The capture of Dvin brought about the end of Georgia's medieval heyday.