Why were modern democracies developed?

Modern democracies developed primarily during the late 1700's and early 1800's, though many continue to emerge to this day (such as Egypt). The prior however were mainly due to the dissatisfaction of the populace in regards to the reigning monarchies of Europe. These revolutionaries argued that the European Monarchs stripped the common people of the most basic rights of man: life, liberty and the pursuit of happiness. Therefore, the people rebelled, almost always violently, and established new democracies that allowed everyone (at this time however mainly land-owning white men) the chance to have a say in their government. Some of these new democracies thrived, such as the United States, while others fell under the reign of dictators, such as France.