User blog comment:Woohoot/Future Lucy and future Rogue timelines/@comment-10543621-20130607083622

How about this?

In the original timeline, with no time travelers, the original Eclipse plan is placed in motion, where they tried using the gate to go back in time to kill Zeref before he became powerful. Unfortunately, that failed and instead brought about the 10000 dragons that destroyed the world in Future Lucy's timeline. Future Lucy herself has no idea where the dragons came from and doesn't know how to stop them, but she goes back in time to warn them of this happening.

In doing so, they eventually figure out it's the gate that brought the dragon, and so Lucy closes the gate, leading to future Rogue's timeline, where no dragons come through, but Acnologia rules the world instead. So, Rogue decides to go back in the past to stop the closing of the gate, and instead take control of the dragons that come through, which leads to the present third timeline.