This is a great question. I would say that conquest and colonization have many difficulties. Let me name a few of them.
First, you need an ideology that actually justifies conquest and colonization. In other words, you need an ideology that allows people to go ahead and do this things, which is very questionable from a moral point of view, especially the idea of conquest.
Second, you will need military power to do this. Many people on all sides will die. For this reason, people will not naturally want to go to war.
Third, if there is victory, there is always the problem of maintaining the new territory, especially if it is far away.
In terms of phases, I would say that you would need an ideology, preparation, and finally maintenance.