The usage of the words left and right to describe political ideas origins from the age of the French Revolution. When the parliament was set up after the war, elected people were settled this way in the chamber:

    _______________
   /               \
  /    __________   \
 |    /          \   |
 | L |           | R |
 |___|     P     |___|

P: the president of the chamber
L: the left side was composed of people against the monarchy (FOR changement)
R: the right side was composed of people for monarchy (AGAINST changement)