Complex sentence: One of Gazan's brigade commanders seized the opportunity to send in the 2nd Hussars and First Vistula Lancers, who wrought massive casualties on the British 2nd division, which suffered the highest casualties, plus they lost five colors, a significant blow to morale and pride.
Split into simpler sentences: One of Gazan's brigade commanders seized the opportunity to send the 2nd Hussars and First Vistula Lancers, who wrought massive casualties. The 2nd division suffered high casualties, plus they lost five colors, a significant blow to morale and pride.