How did the Marxist school of economic theory challenge the Classical theories?

for classical theories look up thomas malthus ...

Also, classical theories say there is an "invisible hand" that guides the economy back to equilibrium. Marx said that the economy should be controlled, thus making to go to equilibrium when you want it to. Only problem is equilibrium isn't a definite spot and depends on market demand and supply. But when the market is controlled these things get trickier. I have only studied oligopoly, monopoly, perfect competition, and competitive monopoly. I would assume that a command economy would be the Monopoly, which determines the price by how much they are willing to supply that is over the marginal cost.