The political Left and Right began with the French National Constituent Assembly of 1789. The Left supported the revolution and democracy, the Right opposed the revolution and supported the aristocracy, and the Democratic Royalists supported a constitutional monarchy. Today there is no aristocratic Right to speak of, at least not in countries such as America. In Britain a constitutional monarchy holds sway in tradition but is politically irrelevant to their democracy. In effect only the Left and democracy remain in the Western world.
The terms Left and Right have evolved over time. The Left came to be identified with socialism, Marxism and organized labor, supported by the social gospel. The Right came to be identified with free enterprise and patriotism, supported by traditional religion. The New Left that arose in the 1960s and 1970s emphasized libertinism, pacifism, and egalitarianism. Non-Left political positions are more varied today: from libertarian to “minitarian” (anti-big business/government) to “corporatarian” (pro-business of any size) to traditionalism.
The basic Left-Right political axis is between egalitarian and libertarian. Political equality cannot be achieved without some loss of liberty, and liberty leads to unequal distributions of wealth and income. So they tend to be trade-offs. The Left is also pushing for extreme equality in which differences such as sex are socially denied. The Right has yet to mount a counter to this extreme egalitarianism.
There are cultural differences between Left and Right, too. The Left is more open to a feeling, people-oriented view while the Right is comfortable with principles and precepts. This works in a negative way, too: the Left attacks people who hold “politically incorrect” views whereas the Right attacks principles that are unrealistic or antitraditional.