Oh, good topic! I always recommend Blackshirts and Reds. Another good one is Michael Hudson's Super-Imperialism. I also intend on reading Settlers soon. Can't neglect to mention Capital, the sections specifically on the conditions of labor in early Britain, with child labor, suffocation, crushing, etc. were genuinely revolting.
As a side-note, I made an introductory Marxist-Leninist reading list, if you find yourself generally interested in the topics I listed above.
No problem!