Complex sentence: He published his first collection of poetry when he was 21 and he had three more published before he wrote his first novel "Blæsende gry" ("Stormy Dawn") in 1934.
Split into simpler sentences: He published his first collection of poetry when he was 21. He had three more published before he wrote his first novel "Blæsende gry" ("Stormy Dawn") in 1934.