The Great Revolutions of Modern History

The great revolutions of the past 300 years have profoundly shaped the social, cultural, political, and military landscape of the 21st century. These epic changes tore down established orders and built new ones in their place. What drives individuals and groups to embrace revolution? At what point does a society decide to revolt? Is there such a thing as a peaceful revolution? Why have some revolutions failed while others changed the world?