A second possibility

A second possibility would be that Civil War will literally trigger the events of Infinity War. And it is hard to see, at this moment, how that could happen. The Civil War strictly regards the Avengers on Earth, whereas Thanos has much more in mind than just a single planet. So"¦

So maybe, just maybe, a 5^th Infinity Stone will be discovered. Or maybe one of the villains (Zemo and Crossbones were already confirmed) is a puppet for the Mad Titan. Or maybe Thanos will make an appearance "“ as we all know, at the end of Avengers: Age of Ultron, he decides to search for the gems himself. And since Vision has one of those gems on his forehead"¦

Anyway, what do you believe? How can this play out in the end?