"Expansion as a permanent and supreme aim of politics is the central political idea of imperialism." (The Origins of Totalitarianism, Hannah Arendt, 1994; page 125).
Imperialism kept the monster that was capitalism growing for a while. That such permanent growth is unsustainable is a reality which is only now, in the 21st century, making itself felt but the desperate measures the world took to try to sustain this addiction found its earliest expression in the 19th century imperialism which shaped the world's politics for the worse.
Economics might push for internally unrestrained growth but mature politics must exercise internal restraint, else it directs the nation into collapse.