The pure foods movement of the 1920s helped undermine natural butter and elevate the status of margarine. In 1923 Congress passed a law that made it illegal to add any other ingredients to butter, even additives that would help make the butter more spreadable. As any toast aficionado knows, margarine is a heck of a lot easier to spread than butter. Suddenly, butter makers couldn’t tweak their products to make it easier to slather on breakfast, but margarine manufacturers could. Margarine’s popularity skyrocketed.

Margarine also got a bit bump from World War II. When wartime butter scarcity forced consumers to switch to margarine, lots of margarine holdouts realized that the improved product wasn’t so bad after all.

See “The Surprisingly Interesting History of Margarine” by Ethan Trex on the Mental Floss website (2010)