In the comics, the Superhero Registration Act was a law passed after a tragic accident involving Marvel characters known as the New Heroes. They tried to stop a villain, but in the process of doing so, got many people killed. This, on top of many other incidents, led the government, backed by Tony Stark, to want to register all people who had a superhero name. Everyone would be registered, and known to the government, thus if another incident happened, they would known who to blame, and who to seek out for proper punishment.
For the movie, Captain America: Civil War, it appeared as though the backbone of the story was going to be about Bucky Barnes, aka The Winter Soldier, as the first trailer mainly focused on that. However, Marvel has released the Sokovia Accords, which is essential the Superhero Registration Act, which says the following:
“In accordance with the document at hand, I hereby certify that the below mentioned participants, peoples, and individuals, shall no longer operate freely or unregulated, but instead operate under the rules, ordinances and governances of the afore mentioned United Nations panel, acting only when and if the panel deems it appropriate and/or necessary.”
There is little doubt that this, along with the loyalty to Bucky, is what will push Captain America and his allies to fight back against Iron Man and his team. We’ll find out how it all goes down when Captain America: Civil War releases May 6th, 2016