Complex sentence: The two regiments of infantry, of 750 men each, were commanded by colonels John Cook and Colonel Joseph Stanton, Jr. and the artillery regiment, of 300 men, was commanded by Colonel Robert Elliott.
Split into simpler sentences: The two regiments of infantry, of 750 men each, were commanded by Colonel Joseph Stanton, Jr. and Colonel John Cook, respectively. The artillery regiment, of 300 men, was commanded by Colonel Robert Elliott.