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The first thing that I want to mention is the critically important role of anti-colonial movements both during and between the World Wars. Although de-colonization did not occur in this time period, there were constant anti-colonial rebellions and attempts to gain independence or, at the very least, some semblance of self-government.

When we look at colonial and imperial history broadly, there was never a time when colonized peoples--to whatever extent we can look at them as a unified whole--accepted their lot. In the early years of colonization in Africa, for instance, various local leaders hoped to use colonizers to their advantage and overturn the current order. Frequently, these were made up of middling leaders that felt they were limited by the power of rulers superior to them. They would sign treaties with colonial powers claiming land that they did not actually possess, and with the force of imperial governments were able to manage their affairs better than before. For example, both Henry Morton Stanley (working for the king of Belgium) and Pierre de Brazza (representing France) both signed treaties with local leaders who claimed to control the same central regions of the Kongo. In exchange, they would be given the right to control their own people under European "protection." The same is true of King Norodom of Cambodia, who signed the treaty that made Cambodia a French protectorate while being exiled from his own territory. These signatories never wanted the French or Belgians to rule over them; rather, they looked to take advantage of European positions to strengthen themselves vis-à-vis other local leaders.

In the early decades, the ways of opposing imperial rule were legion, although they are given far less attention than they should be. Protests and violence are only one of the myriad ways in which colonized peoples rejected their imperial overlords. Other methods include systematically slowing down labor productivity, committing tax evasion, and fleeing forced labor.

By the early 20th century, more organized forms of anti-colonial resistance began to emerge, including the construction of "pan-" movements. Pan-Africanism, for instance, developed largely in the African diaspora, including the United States, following the Battle of Adwa, when Ethiopian armies inflicted a crushing defeat against potential Italian colonizers. Pan-Africanism went on to empower anti-colonial activists who developed more sophisticated methods of anti-colonial actions. Pan-Islamism is another movement that gained strength in the mid-late 19th century and was led by Islamic reformists including Jamal ad-Din al-Afghani, who offered a new form of Islamic modernism capable of mixing Western and Islamic ideas in order to reject Western imperialism. Finally, the 1905 Russo-Japanese War led to widespread excitement in Asia because it showed that Asians were capable of defeating western, imperialist powers and led to a surge in pan-Asianism.

With the onset of the First World War, imperialist powers relied heavily on both the labor and combative strength of colonial subjects. West Africa, for instance, produced numerous raw goods for France and helped fuel its military engine. The Vietnamese, in contrast, were well-known for digging trenches. The French military was also heavily supplied by West and North Africans who often fought on the frontlines and acted as shock-troops. Finally, French factories within metropolitan France were often staffed by colonized subjects, which--by 1917--caused racial panic to take hold of white French citizens. In order to weaken both France and the United Kingdom, Germany strongly encouraged the Ottoman Empire to call for a jihad in the hopes that Muslim colonial subjects would rebel against their colonial overlords. Generally, this did not happen--colonial subjects were promised benefits after the war ended, at times including the possibility of achieving citizenship, and colonial subjects often identified with their metropolitan power.

Nonetheless, there were some large anti-colonial rebellions during the First World War. The Singapore Mutiny of 1915, for instance, was produced by Muslim Indian soldiers who, upon hearing the Ottoman Sultan's call for jihad, took it seriously. The British were unable to put down the Singapore Mutiny on their own, and instead received a great deal of aid from both the Netherlands (which had colonized the Dutch East Indies, or Indonesia) and Japan. Vietnamese nationalists also were active during the First World War and would travel covertly throughout Southeast Asia, aided in part by Siam (Thailand), in the hopes of inciting widespread anti-colonial rebellion.

1919 was a watershed in anti-colonial affairs, thanks in large part to American President Woodrow Wilson's "Fourteen Points." One of the enduring aspects of Wilson's Fourteen Points was that he called for self-determination, presumably for all peoples but, in reality, designed more for central and eastern Europeans under Ottoman and Habsburg control. Numerous colonial delegations made their way to the Paris Peace Conference, including Ho Chi Minh of Vietnam. Paris was a hotbed of anticolonial activity, in large part due to large colonial communities seeking education in the French capital. Zhou Enlai, the first foreign minister and premier of the People's Republic of China during the 1960s, was heavily active in anti-colonial activism.

On May 4, 1919, mass protests broke out globally in response to Wilson's refusal to support self-determination for non-European peoples. In fact, rather than weaken colonial empires, the Paris Peace Conference often strengthened them, and the interwar years are widely seen as the apex of European imperialism. Both the French and British Empires reached their greatest extent in 1920, thanks to their acquisitions of Middle Eastern and African territories under the League of Nation's Mandate System.

The close contact between metropolitan Europeans and colonized subjects led to the rapid spread of nationalist ideas during the First World War, and nationalist ideas would be a game-changer. Rather than rely exclusively on pan-nationalist ideas and vague calls for self-determination (or, among extreme movements, independence), specific territorial boundaries were delineated and the language of citizenship and nationhood strengthened anti-colonial movements around the world. Throughout the 1920s, anti-colonial protests were a constant feature of political life, and brand new political parties with nationalist orientations were widespread. These political parties, built on a European model, acted as a powerful way to organize and maintain political resistance.

In short, you are basically right! Decolonization occurring "after" WW2 is a direct consequence of how WW2 affected European colonialism. Many former colonies had a path to independence as a result of how WW2 changed the power distribution globally.

Erez Manela in The Wilsonian Moment provides a stirring account of how the Paris Peace Conference of 1919, after WWI, was a catalyzing moment in colonial independence movements. President Wilson's language of self-determination ignited the hopes of nationalists in colonized societies, even as hope gave rise to disillusionment when Western leaders in Paris failed to make good on Wilson's soaring rhetoric. But although WW1 did alter the distribution of global power, it largely resulted in Germany's colonies being redistributed among the victors rather than independence.

But independence ideologies and movements gained a great deal of strength between the world wars. Ho Chi Minh, Mao Zedong, and Jawaharlal Nehru all emerged as aspiring leaders of independence movements and would indeed become future leaders of their respective regimes. European countries reacted differently to independence. Britain, for example, had the Commonwealth system and the possibility of "dominion" status for their colonies, which may have helped to ease the transition to independence in some cases. France, instead, generally retained its ideal of assimilating colonial peoples and considering overseas colonies as integral parts of the French Republic.

Despite growing independence movements and some serious colonial revolts, most colonies remained under imperial control under WW2. I can speak more to the course of events in the Asia-Pacific. European powers quite simply could not maintain traditional imperialism as Japan stomped through Southeast Asia and the Pacific. Much of the ideology behind European imperialism was that European superiority justified their tutelage and authority over “uncivilized” and incompetent indigenous peoples. That illusion was shattered when Japan smashed British and French forces in colonial Asia, including the highly public surrender of 80,000 British troops in Singapore. In some places, like Indonesia and French Indochina, former colonial peoples experienced a moment free of European control (even as many began to detest Japanese imperialism to the same extent). The Second World War completely undermined the myth of white superiority, severely weakened the ability of European nations to project power overseas, and launched the United States to a position of global supremacy. The U.S. at this time is a strong proponent of anti-colonial rhetoric and had historically professed itself to be an anti-imperial power (even as the U.S. possessed colonies of its own).

All of these factors precipitated the impossibility of continued colonial control and the spate of decolonization after WW2. Many colonies during WW2 may have realized how weak their colonial overseers were, but were under the control of a different occupying power or still had to contend with the possibility of European powers returning to try to retake control (as what happened in Indonesia and Indochina). In those instances, it would take bloody post-war conflicts for the question of independence to be resolved.

Sources:
(Post-WW1 independence movements) Erez Manela, The Wilsonian Moment.

(FDR anticolonial rhetoric and US visions for a post-WW2 world order) Elizabeth Borgwardt, A New Deal for a New World.

(A good primer on decolonization generally) John Springhall, Decolonization Since 1945

(A history of the First Indochinese War, but provides good context on the Vietnamese independence movement) Fredrik Logevall, Embers of War.