Complex sentence: During the first months of the war, it became the most recognized and popular military organisation fighting on the republican side, and it is a symbol of the Spanish anarchist movement and its struggle to create an egalitarian society based on collectivism and individualism.
Split into simpler sentences: During the first months of the war it came to be the most recognized and popular military organisation fighting at the republican side. It is one of the best known symbols of the anarchist movement in Spain and its struggle for creating an egalitarian society based on collectivism and individualism.