I build an army in a two-dimensional world

Introduction: When the doomsday strikes, a down-and-out scientist discovers a two-dimensional universe in a laboratory dish. In order to explore the secrets of lower dimensions, he does not destroy it, but protects it. However, the invaders discovered the existence of the scientist. In times of crisis, the creatures in the two-dimensional universe regarded the scientist as the creator god and launched a god-protection plan. It's a pity that the plan failed, the scientist's body was penetrated, and the two-dimensional universe exhausted its energy and almost returned to the primitive era. However, the scientist's soul unexpectedly fell into the two-dimensional universe. Next, he will once again lead the creatures in the two-dimensional universe from the primitive era. The tribes of the era moved step by step towards the Stone Age, Bronze Age, and Industrial Age, until they developed into advanced civilization...