Its a big question, but I'll at at least try to make a start.Leftist political parties are characterised by socialist policies, such as universial health care, free education,businesses under more government regulation,more even distribution of wealth,less privatisation of essential services(electricity, water,etc) Plus they are on the left of the political spectrum which is the liberal side if they were on the far left of the political spectrum they would be considered radicals or extreme liberalist
If I'm correct, it comes from the meeting of the National Assembly during the French Revolution. Those with certain opinions sat in the same areas. The Liberals and Radicals sat on the left side, the Moderates sat in the middle, and the Conservatives and Reactionaries sat on the right side.
The political terms Left and Right came about during the French Revolution (1789-1799), referring to the seating arrangement in the Estates General.
Those who sat on the left generally opposed the monarchy and supported the revolution, while those on the right were supportive of the traditional institutions of the Old Regime.
NSDAP National Socialist German Workers Party. NAZI Party
Revolutionary Left Party was created in 1940.
Liberal Left Party was created in 1909.
Liberal Left Party ended in 1945.
Radical Party of the Left was created in 1971.
Left Party - Sweden - was created in 1917.
Democratic Party of the Left ended in 1998.
Left Party - France - was created in 2008-12.
He joined then left the Communist Party.
Party of the European Left was created on 2004-05-08.
Estonian Left Party was created on 1990-12-19.
Democratic Left Party - Turkey - was created in 1985.