Kyokaisenjyo no Horizon is well-known because of the thickness of the volumes. The part II of the second volume is 5.3 centimeter thick. (ref. Akiba blog)
In the far future, humans abandon the devastated Earth and move to the upper world "Tenjo". But Tenjo and the law of causation collapse by a war and humans returns to the Earth, which has turns into an inhabitable planet except for Shinshu area. Shinshu is too small to accommodate all the humans, so they duplicate the area and create "Juso Sekai" in a parallel world. In order to rebuild Tenjo and the law of causation, the returned humans start reproduction of the history from B.C. 10,000. When the reproduction proceeds to A.D. 1413, a war breaks out in Shinshu and Juso Sekai falls onto the original world. The humans living in Juso Sekai lose their land and invade the original world. People in Shinshu surrender and the land is divided by the invaders from Juso Sekai. They try to resume the history reproduction from A.D.1457, but the update of the history terminates in A.D.1648. A rumor of apocalypse begins to spread the world.
The cover picture makes it look like a generic LN adaptation (with attractive character designs, but the synopsis and production company (Have SUNRISE even adapted a LN before now?) are rather more interesting than the cover.
I think I will check it out to see what it is like. It might be good, and the thickness of the volumes is a good sign too (it hopefully means attention to detail).
PS: Are there any mecha in this, or is it a non-mecha sci-fi?