In this article, Robert Montgomery beautifully maps the various steps for understanding Marx’s crisis theory. We begin with what value is, and proceed to the difference between necessary and surplus labor. While capitalists accumulate surplus value, they cannot invest it fast enough to keep up with the rate of productivity. In addition, as workers organize, capitalist are driven to technological innovations so they can dispense with workers. As the technology develops they still face overproduction problems. There is a wonderful graph showing the tendency of the rate of profit to fall over at least the last century.