Complex sentence: Forced into guerilla activism after becoming a fugitive, he became a highly violent and reckless soldier, with the death of many of his friends giving him hatred for the mutant-killing Kreeler police.
Split into simpler sentences: Forced into guerilla activism after becoming a fugitive, he becomes a highly violent and reckless soldier. The deaths of many of his friends fuel his hatred for the mutant-killing Kreeler police.