Answer:
Usually famine causes angst between the weakened civilation so the owners of said territories usually hunt for more fertile land so they can sustain their growing population without having being thrown out of power and slain, its often better to satisfy the people who you govern rather than to exterminate to govern the population steadily.
and to own more land is more money and more power for such rulers, if they own more land they can tax more people, and if they own fertile land they can grow crops to sustain themselves, and the people they govern, satisfying the ruler AND the people.
The Ming emperors made it their capital in 1421 and it remained China's capital till 1912 when the Manchu Empire fell and SunYat Sen turned China into a republic.
C, take hundreds of millions of years to form!
