2nd Super Robot Wars is the firstSuper Robot Wars title to have an actual plotline and had the larval form of what would become the modern SRW battle engine, though it clearly borrows alot from the first game, in this regard.
It began what most fans term the "Classic Timeline", to wit, the "Divine Crusaders War" (or just the DC War) ias the focus of this game. Basically, some alien technology is discovered by a scientist named Bian Zoldark, who studies it and informs the world the crap that will fly unless they're prepared for the alien threat. Since he isn't taken seriously, he starts a war to joltThe Federation's attention. Enter the good guys, who wind up becoming part of SRW's firstXanatos Gambit. Oh, and the first of manyOriginal Generation characters and mecha are featured.