Complex sentence: The most pivotal moment in his life occurred during the war, when he cornered, shot and killed a Korean soldier, who was so terrified of an American soldier with a gun that he wet his pants.
Split into simpler sentences: The most pivotal moment in his life was during his service in the war, when he cornered, shot and killed a Korean soldier. The Korean was so terrified of an American soldier with a gun that he wet his pants.