Oh, I see. I will check it again. I briefly read some Myanmar history because of what's happening right now. I used wikipedia as a quick reading, and I won't be surprised if I am wrong.
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.