First, it really doesn’t matter what we call each system, you can call the older Roman expansionism “Imperialism” and you aren’t wrong. What matters specifically is Capitalism as it turns towards Imperialism. We can call it “Capitalist Imperialism” for the sake of clarity, and what’s important about it specifically is how it relates to Capitalism.

Capitalist Imperialism largely occurs when a Capitalist nation develops enough to where the economy is dominated by large trusts, rather than small competing factories, when bank Capital and Industrial Capital merge into “Financial Capital,” and the only way to continue to compete is to expand outward into foreign markets, essentially where outsourcing labor to the Global South from the Global North occured. This results in a “division of the world among the largest powers,” and was the ultimate cause of World War I and World War II.

Colonialism is similar, but wasn’t impelled by this system of Capitalism. The necessary distinction is the rise of industrial production and export of Capital to the Global South.

If you want to read more, I recommend Lenin’s Imperialism, the Highest Stage of Capitalism. Lenin’s analysis of Imperialism picked up where Marx left off, as Marx had died before he could truly observe Imperialism. Imperialism is actually the reason why Communist revolution never came to the Global North, like Marx predicted, as Imperialism creates a system of bribery for the domestic proletariat and large armies for maintaining this system.

Instead, it came to nations in the Global South, which brought a whole host of questions on how to achieve a post-Capitalist system in countries that were by and large underdeveloped, with large proportions of workers belonging to the peasantry and other non-proletarian classes.