Complex sentence: The Byzantines were forced to fight alone, but the peace with the Arabs allowed them amass their whole army, including the troops stationed in Asia Minor, under the command of the Domestic of the Schools Leo Phokas the Elder.
Split into simpler sentences: The Byzantines were forced to fight alone, but the peace with the Arabs allowed them amass their whole army, including the troops stationed in Asia Minor. These forces were placed under the command of the Domestic of the Schools Leo Phokas the Elder.