How would you explain the rise of the Socialist Party in the 1970s?

In 1981, Francois Mitterand, leader of the Parti Socialiste, won the presidential election in France.  This event stood as an important landmark in the political partys history, not only a political victory for the Socialists, but also was the climax to what was probably the most successful decade for them, both in terms of their rise in popularity and the strength of their infrastructure. The victory can not be pegged down to one single event or action, but an accumulation during the 1970s.

The Socialist Party was founded in 1969 under the definition of a democratic socialist party.  The events of May 1968 struck deep in the hearts of the French people.  The PS was one of the political parties to encourage the protestors to go back to work ….(short extract)