Contrary to the left's insistence that economic conservatives are the true colonialists, it has always been leftist movements that rely on imperialism to advance their agendas. Lenin's "Imperialism" argued that subjugation was the "final stage" of the free market. And eventually looking to cultivate new markets to pursue, financiers would force governments to plant their flag abroad. In reality, the left's need for more servants to feed the government monster drives imperialism. The British Empire heavily regulated transnational trade during its heyday, granting monopolies and taxing its colonies. Germany's Nazi regime and the USSR were both socialist; both were rapacious looters on the world stage. Expansionism is not a solely leftist phenomenon, of course -- but for the most part, full-scale colonization is.
Socialism leads to economic decay. The physics of a decaying economy is like the physics of a dying star: it can explode outward or collapse inward. Since there are no more worlds to conquer, the economy can only collapse inward, as it has in Greece, Ireland and Spain. Who, then, will support the angry masses that march for their "pay" checks?
No one. The coming economic storm will be cataclysmic in its effects. Governments may topple. The population may suffer. This is the legacy of a left, which has purposefully grabbed a tiger by its tail and promised it slabs of raw taxpayer meat. Eventually, the meat will run out, and the tiger will still be hungry.