What would be considered a secondary source about the assasination of abraham lincoln

america opposed the axis powers, because they knew that the united states would be targeted during the war. not only that, but germany (which was an axis power) broke the treaty of versailles, and started developing an army, and started attacking and taking over countries. furthermore, japan, which was allied with germany and italy (who both were axis powers) was attacking china, which was a great ally to the united states.

can you tell me what is it