Complex sentence: Because of the modest nature of these gains, some unions viewed the actions of Keefe as company unionism but in the context of waterside workers coming under attack from employers elsewhere, especially New York City, Keefe's approach was accepted by others.
Split into simpler sentences: Because of the modest nature of these gains, some unions viewed Keefe's actions as company unionism. However, in the context of waterside workers coming under attack from employers elsewhere, especially New York City, Keefe's approach was accepted by others.