The Zerg's expansion was faster than Fang Zheng had imagined.
The reason Fang Zheng chose to summon the Zerg in the world of Edge of Tomorrow was to try out the usage of the Soulstone and to see how the Zerg would proliferate in such a world. In the game, the Zerg required resources like crystal mines and high-energy gas to develop. However, it was certain that these resources did not exist on this world's Earth, so could the Zerg still develop?
As it turned out, that was not a problem at all.
