Complex sentence: Alexios Komnenos, whose army was considerably smaller and far less experienced, tried to ambush Bryennios' army but failed, and the wings of his own army were driven back by the rebels.
Split into simpler sentences: Alexios Komnenos, whose army was considerably smaller and far less experienced, tried to ambush Bryennios' army. The ambush failed, and the wings of his own army were driven back by the rebels.