The point at which democracy is seen to have re-emerged in modern Western Civilization is generally considered to be the Magna Carta in 1215, which established the principle that everyone, including the king, was subject to the law. The Magna Carta also provided a foundation for the development of representative government in England, and it has influenced the development of constitutional law and human rights around the world. The other options you mentioned, the Declaration of the Rights of Man and the Citizen and the American Revolution, were also important milestones in the development of modern democracy, but they occurred much later in history, in the late 18th century.