Complex sentence: Before the act was passed, Benjamin Franklin Butler had been the first Union general to declare slaves as contraband; some other Northern commanders followed this precedent, while officers from the border states were more likely to return escaped slaves to their masters.
Split into simpler sentences: Before the act was passed, Benjamin Franklin Butler had been the first Union general to declare slaves as contraband. Some other Northern commanders followed this precedent, while officers from the border states were more likely to return escaped slaves to their masters.