Complex sentence: It was one of the major political crises during the Third Republic (1871--1940), and it entered the popular consciousness, especially that of the socialists, as an attempt to organize a fascist "coup d'état".
Split into simpler sentences: It was one of the major political crises during the Third Republic (1871--1940). Frenchmen on the left feared it was an attempt to organize a fascist "coup d'état".