Different:
1) Protection time: Mercantilism has no time limit, and infant industry theory has the longest time limit (30 years). Keynesianism believes that it can be used for a short time when effective demand is insufficient.
2) Protection object: Mercantilism and Keynesianism have no specific protection object, while infant industry theory protects infant industries with strong foreign competitors.
3) The purpose of protection: mercantilism-increasing national wealth (currency), infant industry theory-improving the productivity of infant industry, Keynesianism-promoting economic growth and increasing employment.