1. The European's ideas of racial superiority may have directly led the deaths of millions of soldiers from the machine guns. The colonial powers, had experience with and new just how devastating the machine gun when they used it against the indigenous peoples of their colonies. However, many commanders felt that it would not be that effective against well-trained European soldiers. That proved to be a huge mistake and millions of young infantry paid the price as their commanding officers sent them in mass assaults against machine guns.
2. More than any change of heart due to morals, it was the economic and manpower losses of WWI and WWII that made the European powers unable to hold onto their colonies. For example the British had faced unrest in India before, for example the Sepoy rebellion. However, they were able to brutally crush the rebellions and maintain their hold on power. However, in the aftermath of WWII, the British had neither the resolve, the manpower, or the money to continue to try to hold onto India in opposition to the independence movement. Without these World Wars, there is a good chance that India would still be a British colony.
3. The reason that "white" people oppressed so many others was not because they were necessarily intrinsically more immoral, but simply that they had much more power than the others.The examples of the Armenian genocide and the Rape of Nanking from WWI and WWII respectively by people that would not be considered "white" illustrates the sad state of human affairs in that the strong will tend to oppress the weak. This has been going on long before any notion of "whiteness" and will likely go on in the future whatever the status of "whiteness".
4. The post WWII peace in Western Europe was probably due more to the overwhelming superiority of the United States and the Soviet Union vis-a-vis the European powers than of any awakening. Whereas in WWI and WWII, the European powers could imagine beating their neighbors and taking their territory, after WWII, they knew that aggression against their neighbors would lead to a conflict with either the United States or the Soviet Union and they had no hope of winning.