Batman does things his way, Superman does things a different way. They fight about it, and Superman beats up Batman, Batman grins and says, "What are you gonna do, kill me like you killed Zod?" then Superman becomes ultra depressed, but Batman is there to tell him no worries we're bros, let's team up and do it together. They bro up and beat the bad guy. They start the Justice League in this movie at the very end, they are the founding members. Flash swings by in the post-credits.