Imperialism is a fascinating social phenomenon. We see it arise in every nation which develops a comparative advantage relative to a significant proportion of other nations. It also seems to have the tendency of arising more quickly among relatively wealthy nations. The reason for this is obvious: the more wealthy the host the more healthy its parasitical instrument of large scale conquest can be. People are drawn to power and prestige, and in conquest and slaughter many of us find it.
We see imperialism not only among nation-states, but within them. Imperialism within a modern nation-state takes the form of the democratic process. Differing factions war among themselves by means of the ballot, sacrificing ever more of their own power over their own lives in exchange for power over the lives of others. But what they don't know is this is akin to a bargain with a devil, where they will be fed upon by those who appeal to them with their empty platitudes.
Where once relatively wise and free people became rich, all too quickly do their descendants become proud, self entitled, and eventually poor. The imperialism feeds upon itself. The spoils of conquest can never make any society rich in the long term, because destruction is not production. It's really that simple. Those who enrich themselves at the cost of others by means of the state do not create anything, they only cease from coming into being those things that would have been created by others.
All societies that succumb to imperialism consume themselves. But it seems as though prosperity breeds imperialism. Empire is thus its own demise.