The Holocaust(n.大屠杀) is the embodiment(n.体现)of evil in modern times. Adolf Hitler the architect of that genocide(n.种族屠杀). Abused by his father. A vagrant(n.流浪者) at 19. As the only surviving male child, he was adored by his mother. He felt he was special, but became resentful when his mother died leaving him homeless and penniless. A damaged personality, but not yet "evil".
He fought bravely as a twice-decorated (v.授勋) soldier on the Western Front during World War 1. Yet left the army filled with a rage against those he blamed for the humiliation of Germany. Fighting in the trenches(n.战壕)certainly deeply affected any soldier who experienced this hell. Hitler's already damaged mind was pushed over the edge. His resulting Messianic Complex and hatred of the Jews documented in his autobiography "Mein Kampf" for all to see.
Hitler's evil manifested(v.显现) itself after his personality and circumstances collided(v.冲撞) so explosively. If there had been no World War, Hitler would have remained an underachiever(n.学习落后的学生), left in obscurity(n.模糊) in Austria. His "evil" hidden from the world.