Why did americans tend to favor the allies in wwi? (world war 1)

In the beginning of the war, there was a difference of opinion in the US. Many ethnic Germans were rooting for Germany, while Brits, Frenchmen, Serbs, and other Entente-sided peoples supported their respective nations. However, after various atrocities committed by the German Empire such as the atrocities of Belgium, public opinion rapidly shifted against Germany and towards the Entente. The final straw was the Zimmerman Telegram, in which the German Foreign Minister Arthur Zimmerman sent a telegram to the Mexican Government encouraging them to invade the United States, a request which Mexico obviously refused.