Global Tower Defense: I Built a Billion-Strong Dark Legion

He transmigrated to a parallel world, only to discover that it was an age of dark upheaval! Humanity across the globe was building tower-defense walls to fend off invasions by hordes of dark creatures, including zombies, vampires, giant beasts, and werewolves! Luo Xiu rose to power with the System, leading all of humanity in building defenses while summoning and forging a mighty dark army of his own. With smoke billowing across the land, this age would be ruled by Luo Xiu...