What did americans call hamburgers during world war 1?

"Liberty steaks"

The strong anti-German sentiment that existed in the United States during the First World War motivated an effort to refer to hamburgers by a non-German name.  America was fighting for liberty -- "to make the world safe for democracy," in the words of President Woodrow Wilson.  So "hamburgers" began to be referred to as "liberty steaks" and another German-named food, sauerkraut, was called "liberty cabbage."

Something similar occurred in the United States when France expressed opposition to the US pursuing war in Iraq in 2003.  Some began referring to French fries as "freedom fries." 

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