Right vs Left

The terms "left" and "right" appeared during the French Revolution of 1789 when members of the National Assembly divided into supporters of the king to the president's right and supporters of the revolution to his left. (The seating may have been influenced by the tradition of the United Kingdom Parliament, where the monarch's ministers sit to the speaker's right, while the opposition sit to his or her left.)
 
Those who were loyal to religion and the king took up positions to the right of the chair so as to avoid the shouts, oaths, and indecencies that enjoyed free rein in the opposing camp". However the Right opposed the seating arrangement because they believed that deputies should support private or general interests but should not form factions or political parties. The contemporary press occasionally used the terms "left" and "right" to refer to the opposing sides.
 
At least this is one cause. . .