Ancient Greece is regarded as the birthplace of democracy, in particular Athens (5th century BC). Small Greek city-states enabled direct political participation, but only among its citizens (a small political elite).
As societies grew, more refined systems of representative democracy were needed. In a feudal system, the king selected tenants-in-chief to provide counsel. In late 13th-century England, a parliament evolved, but remained answerable to the monarchy. Changes in land ownership and the growth of a mercantile class widened the representative base of parliament.
The Parliamentarians' victory in the English Civil War was, in general terms, a victory for parliamentary sovereignty. A fundamental shift in emphasis was the transition from natural law to natural rights, as expounded by John Locke: in addition to responsibility (to crown or church), people possessed inalienable rights.
Rousseau developed these notions into the social contract, which influenced the French and American Revolutions: government was limited by law from impinging on individual freedoms.
During the 19th century, the franchise was extended. In the 20th century, democratic representation has been a matter of debate and sometimes bloody dispute. Common to modern liberal democracy is the principle of free multi-party elections with universal adult suffrage.
From CREDO democracy from Philip's Encyclopedia
Image from Library of Congress