Soon after the end of the Pacific War, many of the countries, such as Vietnam and Indonesia, occupied by Empire of Japan during the Pacific War either achieved independence or started wars of independence that eventually led to their independence.
Was this rapid decolonization of Asia a direct result of the Empire of Japan starting the Pacific War, Or was the decolonization of Asia inevitable already before the Pacific War?
Also, did the decolonization of other countries in Asia contribute to the Independence of India in 1947 in any way?
This is a extremely interesting question! As I am sure you know, a large amount of Asia was controlled by European empires, and to some extent, the United States, prior to the expansion of the Japanese, who essentially replaced the Western Allies with themselves.
In 1941, the United States signed the Atlantic Charter, which set out a vision for the post war world, that included the right to self determination. Eventually, a large majority of Western Allies signed this treaty. Upon the end of the war, there were attempts by some of these signatories to return to their former colonial holdings and resume power, specifically France in Indochina, and the Netherlands in modern day Indonesia. There was a general disregard by Americans of the concept of Empire, ignoring their holdings in the Philippines.
However, during their absence throughout the Japanese expansion, native resistance movements had not only been set up, but had also gained a large amount of legitimacy throughout the native population. They also found themselves with a large stockpile of available arms from the vanquished Japanese, some of which had been gained in a last ditch spite effort from the Japanese Army.
Also, the Japanese had attempted to quell dissent stemming from their invasion by claiming that their efforts was taking "Asia for the Asians", even though they essentially were a replacement for the former colonial masters.
So there were two massive factors in the decolonisation of Asia. Firstly, the signing of the Atlantic Charter. Though it was thought to be only in regards to Europe, the Empires could hardly claim international legal legitimacy if they held Asia to be exempt from this. Secondly, the power vacuum left upon the expulsion of Japanese forces and the return of Europeans, along with a large amount of armaments and a left over by product of Asian nationalism demonstrated by the Japanese lead to the rapid decolonisation of Asia.
In regards to whether this was inevitable, I do not feel comfortable answering this. I would posit that WWII was a massive influence in the decolonisation of the post war years, and may have been critical to its development, though with any hypothetical question, it is impossible to answer.
In regards to India, independence had been an issue for several years, if not decades prior to the war, and though I do not have my sources on me at the moment, I believe that it was negotiated during the war. I can fully answer this to the best of my understanding in a couple hours, when I have found some of my sources.
Sources. D J Lu, 'Imperial Rescript on Surrender, 1945' in Sources of Japanese History, Volumme Two.
C Bayly and T Harper, Forgotten Armies: Britain's Asian Empire and the War with Japan.
D P Chandler, In Search of South East Asia: A Modern History
Askashi Yoji, 'Japan and Asia for the Asians' in Japan Examined: Perspectives on Modern Japanese History
Goto Ken'ichi, 'The Dynamics and Legacy of Japanese Wartime Rule in Indonesia' in Tensions of Empire: Japan and South East Asia in the Colonial and Post Colonial Word.