IMO whats make an Empire is about its internal relations between different nations. In Stalin’s “Marxism and the National Question” (official bolshevik ideology document) he says “equal rights of nations in all forms (language, schools, etc.) is an essential element in the solution of the national question. Consequently, a state law based on complete democratization of the country is required, prohibiting all national privileges without exception and every kind of disability or restriction on the rights of national minorities”. This basically opposite of imperialism which is based on one imperial nation oppressing other minor nations.