Complex sentence: Trumball understood how uneasy it was for the three men on a different sides of the brutal war to overcome they differences, and to work together as a climbing team, because on Everest ability to work as a team could be a matter of life and death.
Split into simpler sentences: Trumball understood how uneasy it was for the three men on a different sides of the brutal war to overcome their differences, and to work together as a climbing team. On Everest, the ability to work as a team is often a matter of life and death.