Leftism as a political orientation gained its name during the French Revolution. The aristocratic members of the Estates General or National Assembly would sit in the place of honor to the right of the Speaker, while the commoners would be relegated to the left. From this, "the right" came to mean support for aristocratic interests, or the ancien régime, while "the left" implied opposition to the same, such opposition including proto-laissez faire free marketeers (who in modern America are considered to be rightists) and communists (that is, commune-ists). At the time, the defining point on the ideological spectrum was the old order, on the right. On the near left stood people holding views similar to those of Edmund Burke, and on the far left massed a host of competing alternatives.
Traditionally, the left side of the political spectrum begins with modern liberalism, extending through social democrats and moderate socialists into communism. Many have disputed this arrangement as simplistic; they argue that Russian-style communism does not really belong on the left and should be viewed independently of the conventional spectrum or placed in the right as authoritarian dictatorship. This association has often been used by critics of democratic socialism or left-liberalism to argue that the political left is tarred with the crimes of bolshevism.
The European left has traditionally extended into Communist parties, which have sometimes allied with more moderate leftists to present a united front. In America, however, the left has been defined by labor unions and New Left activists rather than 19th century socialist ideas.
The 'New Left' has had varying degrees of unity since its rise in the 1960s, and encompasses several movements such as feminism which are not always recognized as leftist. Greens often deny that the 'left' label provides any useful cover or coherence, and build their green politics on a different set of assumptions. Usually, that local control is better than central, and only a few issues benefit from global unity. This further erodes the 'left' message.
Many critics of the left have said that leftist movements lost their mooring after the fall of the Soviet Union. Most leftists respond that they have never taken their inspiration from the Soviet model and were happy to see the USSR's system collapse -- as leftist writer Michael Albert put it, "one down, one to go".
Some leftists also subscribe to post-modernism and Nietzschean philosophies. This has been remarked on both by the right, which generally sees it as an indication of the poorly thought-out, fashionable nature of leftism, and by critics on the left who say postmodernism makes no sense and offers no useful political lessons.