You need a more united people to works towards a target.
As for the British Empire, it is crumbling after WW2. Most colonies are demanding for independence and is not restricted to India. You are making a poor comparision.
Are you saying that the Indians are not united ? The same can be said of the PRC as well! Even Japan is not "united" as you imagine it to be.
In a democracy, people have different opinoins and different political views. But all share a common understanding and common goals. Unlike Communist nations where everybody says the same thing and nobody has the courage to disagree, democratic nations have differing opinions and differing political viewpoints but that doesnt mean they dont share greater common interests. How else do you explain that 1 billion odd Indians have faith in the ballot box and exercise their franchise every 5 years and the fact that India with so many different cultures and languages is thriving today after more than 200 years of colonial rule ? Or that one man could motivate more than 150 million disparate people to join together in the fight for freedom through non-violence (something that had never been done before! )
You like most chinese underestimate the power of freedom and democracy because you fail to realize the moral strength it endears to its citizens. They might be at odds today and have very little in common but all share the ideas of democracy, freedom, equality, liberty etc. That makes them more "united" than you realize!
As for the British Empire, India was not just another "colony", it was its greatest colony! And despite the freedom movement, they were still able to conscript 2 millions troops to fight WW2 successfully across Africa, the ME and Asia. So India got its freedom not "because" of WW2 but rather "inspite" of WW2 !
Also, the British Empire was actually stronger militarily after WW2 than it was before !