For those that don't know, the Injustice Series is also a comic book series that is owned by DC Comics and one that even coincides with the popular video games. If players were to compare the comics for both games in the series thus far, they will notice that most of the content (though not all of it) of the graphic novels are also incorporated into each of the games.
The first four chapters of the Injustice 2 Comic Series even serve as a prequel to the game, properly bridging Injustice: Gods Among Us to Injustice 2. Now the Beginning of Story Mode this sequel game also tries connect the two stories, but if a player was so wanting to know the full details on what happened from the original game to its predecessor, then they need look no further the the Injustice Comic Series themselves.