Complex sentence: Roman influence gradually crossed the peninsula over a prolonged period of two centuries, and therefore some societies were crushed initially, others succumbed after a long assimilation and others survived in uneasy alliance alongside the Roman empire for some time.
Split into simpler sentences: Roman influence gradually crossed the peninsula over a prolonged period of two centuries. While societies were crushed outright, others succumbed after a long assimilation and yet, others survived in uneasy alliance alongside the Roman empire for some time.