Before I start this article, please be aware that it will contain SPOILERS for Captain America: Civil War. Please, if you haven't seen the movie, do so before you read.
In some ways, Captain America: Civil War seems to end like most superhero movies. The bad guy gets defeated, the good guys are all alive, and we're back on the road to the next big Marvel movie.
Unlike any previous Marvel villain, however, Helmut Zemo accomplished something that Loki, Ultron, and every other villain so far has failed to do.
Yes, he's imprisoned, and yes, all the Avengers are alive, but they are definitely not well. Bucky is back on ice. Cap, Wanda, Hawkeye, Scott and presumably Widow are all on the run as fugitives from most nations on the planet, with only the potential support of T'Challa and Wakanda.
Tony feels betrayed by his best friend. Vision is dealing with his ever-increasing humanity and the fact that he made his first mistake — a mistake that nearly cost Rhodes his life, and did cost him use of his legs. And of course, Uncle Ben is still dead (though that one's probably not Zemo's fault).
That was Zemo's only goal. To break the Avengers, to show them that one truly determined man can take them down. Not only that, but he didn't even have to do the heavy lifting. The team did that to themselves.
The last we saw of Helmut Zemo, he was sitting in his cell, smiling at his success. He didn't need to get away, he didn't even need to hide. He didn't mind them finding him once it was too late for the team. Zemo was fulfilled. But when he moved to take his own life, the Panther's vibranium-sheathed hand stopped the bullet.
Zemo's continued life, however, means that his goal is still in mind. He'll have a lot of time in that cell to plan how to further crush the Avengers. That's also a lot of time for another mastermind to plan.
Remember Zemo's one defining aspect? His success where both god and machine failed? That will not go unnoticed by the Mad Titan.
Thanos sought to impose his will on Earth through various manipulations including Loki's invasion and the creation of Ultron. And though he has pledged to "do it myself," that doesn't mean he'll step out of the shadows instantly.
Avengers: Infinity War Part 1 is set to be retitled, and I think this will reflect the first stage of Thanos' more direct intervention. And I think he'll go to the one man who already beat them.
Thanos could very easily set Zemo free and have him pull together a team (Masters of Evil, anyone?) to extract the Mind Stone from the Avengers, and potentially join him to acquire other Infinity Stones. After all, if Zemo could break them alone, he's not a bad bet to beat them completely with a true team.