What impact did WWI have on colonies and colonialism?
For the most part, I would argue, WWI had very little impact on colonies and colonialism. In theory, WWI would have helped to do away with colonialism, but in reality it is hard to argue that it actually did.
In a sense, one might expect that Woodrow Wilson’s 14 Points would have meant that WWI would have helped to end colonialism. For example, in Point XII, Wilson said that the areas that had been non-Turkish parts of the Ottoman Empire
should be assured an undoubted security of life and an absolutely unmolested opportunity of autonomous development.
This implies that they should have been allowed to become independent. If those areas were to become independent, then logically other areas should have the same chance.
However, this is not what happened. Instead, essentially everywhere that had been a colony before the war was still a colony in practice after the war. Many areas, like the former Ottoman territories or the former German territories in Micronesia became League of Nations mandates, but those areas were, in essence, simply colonies of the countries that were supposed to be running them for the League. Other places, like French Indochina and British India, simply remained in the hands of their pre-war colonial masters. All in all, it is hard to say that WWI had much of an impact on colonies and colonialism, regardless of what Wilson said in his 14 Points.
Colonial rivalry was one of the causes of World War I. Tensions developed and relations worsened between European nations as they jockeyed to build colonial empires throughout under-developed portions of the world such as Africa and Asia. This worsening of relations and distrust of one another was one of the reasons the Europeans entangled themselves in the complex alliances which plunged the world into full-scale war.
Consequently, one might expect that world leaders would recognize that colonialism was dangerous. As Pohnpei397 metioned, U.S. President Woodrow Wilson advocated that some former colonies (those controlled by the "losers" of the war) should be given the ability to govern themselves. However, by and large the European leaders were not yet interested in granting their colonies independence. Thus, the Treaty of Versailles did little to change colonialism except to redistribute the colonies to other nations. It would take the utter devastation of World War II to cause Europe to realize they no longer had the ability to govern vast colonial empires.
To the victor goes the spoils, and that in effect was the result of the First World War on European colonies. The Treaty of Versailles called for the colonies of the Central Powers to be given to the newly formed League of Nations. Germany, the Austro-Hungarian Empire, and the Ottoman Empire all lost their colonial claims with Great Britain and France receiving the lion's share of their holdings. Great Britain took a controlling interest in Iraq and Palestine, while France took possession of Lebanon and Syria. The remaining portions of the Middle East were combined to form the Kingdom of Saudi Arabia.
The post World War I scenario was highlighted by the fall of some colonial powers and the rise/peaking of some others. A redistribution of colonies and territories took place following the Treaty of Versailles. Germany was the biggest loser, while Britain and France gained the most new territories. Britain gained Palestine and Iraq; France got Syria and Lebanon; Australia got German New Guinea and New Zealand gained German Samoa.
Another important change was the freedom of a number of former colonies, including Estonia, Finland, Latvia and Lithuania—all from the Russian Empire; Austria and Czechoslovakia were split from the Austro-Hungarian Empire; etc.
The new state of Saudi Arabia was also formed from parts of the Arabian Peninsula.
World War I led to circumstances that began the process of independence in a number of colonies, mostly from the British Empire. The most important was the freedom of India (and creation of Pakistan and later Bangladesh).