"Capitalist use of technology would extract surpluses from the labor of the proletariat, leading to greater concentration of wealth and the progressive immiseration of workers. The bourgeoisie who ran this system could not, despite their wealth, consume everything that it produced, while the proletariat whose labor made it possible were too poor to buy its products. Ever increasing levels of inequality would lead to a shortfall in demand, and the system would come crashing down upon itself." -- p. 436
Thomas Sowell, who wrote his dissertation on Marx and published an entire book on Marxism, gives the true picture:
"Crises are inherent in capitalist commodity production because producers cannot accurately predict the demand of the consumers or the supply of other producers...
"Neither underconsumption nor a permanent 'breakdown' plays any role in this picture..." -- Marxism, p. 92 (emphasis mine)
Marx and Engels in fact ridiculed underconsumptionist theories, by noting that the bust occurred precisely when wages were at their highest. Their theory is one of coordination failure, not of underconsumption.