But Myanmar was never a strong and unified nation. Arguably the Mongolian invasion was an exception due to their powerful military forces, the cultural impact made by the Mongolians was minimial. People did not build powerful economy or anything like that, despite their geographically strategic location. So what happened there?

 

 

Despite the fact that China was much bigger than Burma, Qing was seriously corrupted, and many of their civil servants were addicted to opium. Declining Qing dynasty created power vacuum, allowing different factions rise and fight for the supremacy over Qing dynasty. Japanese attack in Manchuria was an example. Burma was not struggling in civil war, especially due to the previous foreign attacks by Portgugese and French... and were more prepared than Chinese to resist the Europeans more effectively. Plus, the resentment towards Britian was quite strong in Burma. In fact, when Japanese armies occupied Burma in WWII, they were greeted as heroes. Majority of Burmian people supported Japanese troops to attack India, and later fought agains the British and US counterattacks. Burma was among the few countries to reject offer to join Commonwealth.

Yes. Burma ( Toungoo ) also defeated the Portugese attempts.

 

Burma must have prospered well in the old days, if we look at the material data( often closer to a non-ideological truth )

 

 

The above is some 10 % (!) of the 1000 year old city temple city  Bagan. As we can see , it reached the horizon, larger than many modern cities. There several of such gigantic projects.   They took  decades/centuries of intense labour , involving 10.000-100.000 s people.