Before getting into that, infamy is when people know a person for bad quality or deed. It can also be known as Notorious.
Napoleon was a French general. He was very skilled in leading his army to victory, even despite the circumstances. One time, Napoleon fought two forces at the same war and won. He was known as a supreme war leader, and they made him the Commander in Cheif of his nation. As a result, soldiers lost their lives, and people started to lose hope in Neoplean. He had excellent talent and leadership experience, for example, living off the land to boost the soldiers' speed. This caused his army to be at multiple places at once, enabling them to strike forces simultaneously. All this caused other nations to team up and stop Napolean because of all the killing he has done.