The French Revolution and the Napoleonic Empire instilled fear in the hearts of every European monarch. Once he was finally removed from power, they sought to prevent this turn of events from ever happening again in Europe. Toward this end, they passed a number of reactionary policies, such as Great Britain's 1815 Corn Law, which secured profits for British nobles and prevented competition from imports.
Such laws--designed to protect the power of the elite--hurt the middle and lower classes by raising food prices. This hurt the poor because they could not afford to survive, and it hurt the middle class businessmen because they were forced to pay their employees higher wages so they could afford food.
Consequently, the middle and lower classes began to team up to attack the European monarchies and aristocracies. This political movement gave poor workers their first taste of political organization, and Karl Marx believed it prepared them to overthrow the middle class, along with the monarchs (as he and Engels wrote in the Communist Manifesto). Thus, the reactionary policies of the post-Napoleonic European monarchs actually resulted in the Marxist revolutions of 1848.