The Enola Gay was the plane for Hiroshima.
The assumption that the empire could be ruled and united under the emperor was challenged as many different families and factions fought for control and continuously engaged in warfare and intrigues in order to gain or consolidate power.
Because of the lack of central control and stability, some of the grand projects envisioned by rulers like the Grand Canal or the Great Wall fell by the wayside because of a lack of funding and again the lack of control over the various factions.
This led in some ways to a return to looking inward and working within familial groups and locally controlled provinces. The assumption of a national identity was slowed and even stopped in some places as different provinces again started to look out for their own interests and stood up to fight for them against anyone not willing to allow them that freedom.
I’m pretty sure it’s the Polio Vaccine
