There are certain milestones to be reached before the ultimate goal.

Marx warned of the problems arising from only portions of the world converting to communism. The world had to be sufficiently advanced in technology, to support one person being a doctor one day and an engineer another. If even one of the societies were capitalist, the move towards communism would fail, because there would always be room for that one society to tempt and bribe the communist society towards failure. A universal labour class consciousness, and class conflict would need to occur. Spencer, on the other hand, warned that these milestones were the intraclass conflict, struggling to come out on top.