Marxism says that capitalists want to exploit the workers as much as possible and make their pay as low as they can. The capitalists do this to create as much profit for themselves as possible, as quickly as possible. Workers, on the other hand, have to struggle to keep their wages up and to keep the "rate of exploitation" low, so that they can live more peaceful lives. This is what Marxism calls "class struggle": where workers and their bosses fight against each other to gain for themselves.