Through most of the 18th century, democracy was mainly associated with what would today be called the far left (see Enlightenment). Historian Richard Hofstadter reports that in the debates that led to the American constitution, worries were expressed that the people might just vote to redistribute wealth. This led to an elaborate system of checks and balances designed essentially to limit democracy. (Of course, I am oversimplifying. Democracy can have serious issues, as Plato would remind us, and a constitution is a good thing overall, as Aristotle would remind us.)
The American and French revolutions temporarily gave the cause of democracy more of a mainstream status. But after the 1848 events in Europe led to more worries over possible redistribution of wealth, further progress in the direction of democracy again depended on mainly the activity of the left.
In the late 19th and early 20th centuries, the strongest support for democratic advances worldwide actually came from the socialist movement, which had an amazingly vibrant and fertile tradition of rational debate on principles of theory and practice. (After Stalin and Mao and their imitators and successors, it may be hard to remember this. Stalin brutally suppressed all debate and especially exterminated criticism from the left, while systematically betraying everything the movement had stood for. Mao was even further removed from the historic rational tradition of left-wing social democracy. But all such monstrosities do nothing to invalidate the rational ideas of social justice they travestied.) (See also Economic Rationality?; Rights; Justice in General; Authority, Reason; The Autonomy of Reason; Honesty, Kindness; Intellectual Virtue, Love.)