Why Did the End of the World Happen in Ancient Times?

There are only three months left before the end of ancient times. The bustling capital is singing and dancing, and the people live and work in peace and contentment, but they don't know that a catastrophe is about to come. In the last life, the mountains and rivers collapsed, famine and epidemics swept through, and almost everyone died at the hands of unknown creatures. Once reborn, the system assisted, secretly plotted, and dealt with the nobles of the palace. When the end came, she was already the overlord of one base. [Main career, no cp, the story of how to develop a generation of lords]