Complex sentence: It was Casares' effort, for which he won the 1941 First Municipal Prize for Literature of the City of Buenos Aires, and he considered it the true beginning of his literary career, despite being his seventh novel.
Split into simpler sentences: It was Casares' effort, for which he won the 1941 First Municipal Prize for Literature of the City of Buenos Aires. He considered it the true beginning of his literary career, despite being his seventh novel.