The idea of a political spectrum stems from deliberative bodies in which groups of like-minded men would sit on opposite sides of a chamber, which gave rise to terms like "left" and "right" being attached to the views of the men on those sides.
The earliest known left-right classification was that of the National Assembly in France just before the French Revolution. Members who supported political rights for all classes of society,[Citation Needed] would sit on the left side of the assembly hall in which they met. Members who supported the monarchy, would sit towards the right. Those who had been offended by their own party would frequently stand up and walk over to the other side of the hall in order to make a political statement.
Historian Arthur M. Schlesinger, Jr. has said the spectrum theory was "adequate to the political simplicities of the nineteenth century, when the Right meant those who wished to preserve the existing order and the Left meant those who wished to change it. But the twentieth century, here as elsewhere, introduced new ambiguities." 
The original definition referred to Church and State issues from the late 18th century Enlightenment period. At its root was faith vs. rationalism, or the Church vs. secularism. The so-called "right", defined as "traditional interests" refered to the Church & monarchy who ruled by the Divine right of kings, and the so-called "left" constituted secular elements challenging the Church's longheld influence over civil government. These definitions have always been problematic when attempting to assign Western notions of "left and right" to societies which traditionally have no conception of separation of chuch and states, such as in Islam  or Czarist Russia.
The monarchy and titled nobility became known as the "right"; this idea however has been disabused in the United States where a landlord class of titled nobles never existed, and in fact is specifically prohibited by the U.S. Constititution. Hence Europeans today, based upon their own cultural idioms and history, have an extremely discolored view of what the "American right" is.
The "left" is often described as advocating "change" of traditional systems and institutions of a society, however the leftist regimes of Cuba and North Korea stoutly resist changes other leftist regimes abandoned 20 years ago after seven decades of stagnation and exploitation of the oppressed common people by a privileged leftist ruling elite.
At the time of the French Revolution, when the existing order, or Ancien Regime had been overthrown, the idea of nationalism did not exist throughout most of Europe. During the violent years of 1793 and 1794 in France, a love of the Patrie, or the nation, was cultivated to replace the foundations upon which society had been built under the old order. Under the stimulus of this movement for national unification, Catholicism was faced with the competition of a worship of national patriotism. Nationalism grew out of this new will to construct and shape the political community. 
This transmutation of a love of God to a love of "the people" as being the basis for a social and political system spread across Europe and other parts of the world during the nineteenth century. In Germany it became a recognition and conciousness of "das volk", later in Russia it was a dedication to the "narodny". By mid-century, Socialism as a doctrine sought to overthrow the existing order of society, dominated by the Church and aristocracy, by promoting atheism and nationalism. The basic tenet was to replace the individual's committment to love and serve God with the individual's committment to love and serve the collective society.
- Not Right, Not Left, But a Vital Center, Arthur M. Schlesinger, Jr., New York Times Magazine, April 4, 1948.
- The Political Career of Muhammad, Arnold Toynbee, A Study of History Annex II TO III. C. (ii) (b) p. 466.
- John Hall Stewart, A Documentary Survey of the French Revolution (Macmillan, New York, 1963).
- David A. Bell, The Cult of the Nation in France: Inventing Nationalism, 1680-1800, (Cambridge, MA: Harvard University Press, 2001). 
- a 2-d view with left-right based on US politics and a novel vertical axis