6. Infinity Stones On Earth
It could turn out that something as simple as another Infinity Stone emerging in Captain America: Civil War connects it to the huge upcoming Avengers: Infinity War event - or the fact that Vision already has one and will be using it in battle again. While it might seem unlikely that a new one would emerge on Earth, the fact is it definitely could - they could turn out to be anywhere in the universe, after all, and it could have been hidden for hundreds or thousands of years - and it could turn out to be in the possession of one of the characters appearing in Captain America: Civil War. If indeed another Infinity Stone does appear on Earth (remember, the aforementioned Vision already has the Mind Stone embedded in his forehead, so it could just be as simple as his continued use of it helping to trigger the Infinity War), it would give Thanos another reason to come to Earth in the Avengers: Infinity War movies - the powerful villain has expressed his intention to gather them for himself, following the failings of his henchmen, after all.