I would say the easiest way to begin is to divorce the historical/political idea of empires from Lenin's ideas of imperialism. There is a reason he called it "the highest stage of capitalism" after all. Capitalist imperialism is drastically different from pre-capitalist imperialism.

You can however, supported by historical reading, begin to see similar trends in the politics and economics of past empires, and ironically empires make a lot more sense as a political unit when you think about them from a materialist perspective. Why did the Romans and the Parthians fight over Armenia? Did crusaders invade the Levant to secure the holy land for pilgrimage or for Italian spice merchants? Why did the Mongols conquer so much? As happybadger says in his reply, this is just history repeating itself, but I would posit that it might be a good idea to firmly understand imperialism as a stage of capitalism (as it is now) first before you try to dig into the imperialism of historical empires because it will be confusing to try to understand imperialism as a universal phenomenon through different modes of production.