One could say that World War I put in place the process of decolonization that would eventually bear fruit fifty or sixty years later. Once the war had been concluded, the general consensus among the victors was that nations must have the right of self-determination. President Wilson of the United States was particularly enthusiastic about this right, which he strongly promoted during the talks that would give birth to the Versailles Treaty.

In immediate terms, however, the right of self-determination did not apply to colonies in what we would now call the developing world. Under the terms of the Versailles Treaty, Germany was stripped of its overseas colonies, but this didn't mean that they would subsequently enjoy the right to determine their own affairs. Instead, they were given to the Allies, who proceeded to treat them in much the same way as they did the colonies that they already owned.

At this stage, then, national self-determination did not apply to the colonies, for the simple reason that the colonies weren't nations but pieces of territory owned by imperialist nation-states such as France and Great Britain. Nonetheless, the noble vision behind the concept of self-determination would, in due course, inspire successive generations of anticolonial activists in their struggle for freedom.

World War I was caused in a large sense by the imperial contests of the late nineteenth and early twentieth centuries. As the great empires of Europe butted up against each other and competed for a dwindling number of available lands to be colonized, it seems inevitable that a conflict would take place.

After the war, the nature of colonialism began to change. The losers, namely Germany, the Ottoman Empire, and Austria-Hungary lost their colonies. In some cases, the victors took them over. In other instances, new nation-states were established out of the former colonies. Although it would really be the period after World War II that would see the thorough decolonization of much of the globe, this move to establish more independent nations placed the notion of self-sovereignty more firmly in the minds of colonized peoples.

Throughout World War I, the combative empires regularly called on the people of their colonies to contribute to the war effort. After the war, a period of colonial reforms was implemented by the English and the French, partly as a way to reward the colonies for their service and partly to mollify colonial veterans who might now start demanding more freedoms. For instance, even before the war ended, the British government announced that it would start gradually transitioning more authority over to local leaders in India. In Algeria, the French promised to allow more local autonomy as part of their effort to recruit more Algerians into the military. However, these were often half-measures aimed at appeasement rather than actual change, and the nature of colonialism remained much the same in the interwar years.

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.

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.

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.

What impact did WWI have on colonies and colonialism? 

World War I had very little impact on the institution of colonialism as a whole.  It did have impacts on specific colonies, but it did not change the fact that colonialism was widespread nor did it lead to any serious change in the way that colonialism was carried out.

After WWI, many colonies changed hands. German colonies in Africa were split up and given to such countries as Belgium, Portugal, and Britain.  German territories in Micronesia were officially put under League of Nations mandates, but were essentially given to Japan.  Ottoman territories in the Levant were given to Britain on the same basis.  

What did not happen was any widespread independence.  Vietnam pressed for independence from France but did not get it.  India did not become independent of Great Britain.  This was a war that caused changes in what countries controlled what colonies, but it was not a war that seriously challenged the idea or practice of colonialism.