From Action Comics #2 (July 1938). Written by Jerry Siegel; drawn by Joe Shuster.
In his earliest appearances, Superman didn't fight supervillains; he fought against social injustice like war profiteering, usually by exposing the greed of whomever was behind the injustice and them forcing him to stop. Hence his "never ending battle for Truth and Justice." The American Way part wouldn't be added until he became a rallying point for patriotism during WWII.