Complex sentence: The mix of combat and support service units was, in theory, to be roughly equal between both groups, though this caused tension between the Department and operational commanders, with the latter generally unwilling to provide places for black combat units.
Split into simpler sentences: The mix of combat and support service units was, in theory, to be roughly equal between both groups. This caused tension between the Department and operational commanders, with the latter generally unwilling to provide places for black combat units.