This is a difficult question to answer, because all nations are different. However, there seems to be some commonality. First, there is a feeling of exceptionalism. If one group colonizes another, then there is the idea that the ones in power are somehow better than the ones are colonized. We can say that there is a sense of pride.
Second, the nations that colonize are a bit wealthier, at least for the time being.
Third, in time the people who colonized others feel a sense of guilt. People cannot go very long without seeing the inherent injustices of taking over another group.