Complex sentence: Tom Hayden, one of the leaders of Students for a Democratic Society, encouraged protesters to move out of the park to ensure that if the police used tear gas on them, it would have to be done throughout the city.
Split into simpler sentences: Tom Hayden, one of the leaders of Students for a Democratic Society, encouraged protesters to move out of the park. This would ensure that if the police used tear gas on them, it would have to be done throughout the city.