The trailer seems to hint at multiple asteroid impacts. That, and the vaguely Stonehenge thing, make the assumption that this is something of a return to the strangereal continuity and a bit of a remake of AC4 more likely to be true.
AC4's backstory is that Earth was under threat of asteroid bombardment, so the nations of the world built an array of superweapons designed to kill it. This thing was called Stonehenge, and had several large railguns shooting nuclear munitions (or munitions that looked suspiciously like nukes, anyway). After the impact was over, the country in which Stonehenge was built took control of it, and used it as an airspace denial system to dominate its own continent.
