Haven’t seen the movie yet, but in the comic books, a team of young heroes were filming a reality show, attacking a super powered guy and ended up inadvertently killing a bunch of children. The government stepped in and said “Ok, we really need to have every super-hero get registered. We need to know everything about them including secret identities. Spider-man came forward and unmasked and discovered that’s a bad idea as his enemies started targeting his family and friends. Tony Stark built a big flying outer space gulag and with the force of the government he tracked down any super-hero who didn’t register and work for the government and imprisoned them. Captain America was really against him on that.
Tony’s always had the “I’m richer, smarter, and hotter than you” attitude n the comics and some definite fascist tendencies.
The movie doesn't paint either as a "good guy" or a "bad guy". They're just two guys that seriously disagree on what the right thing to do is.
And obviously, the first order for the group that registered was to bring in the group that didn't register -- hence, the Civil War.