Complex sentence: While he was still a student, he composed a number of ballads and published his first collection of poetry in 1898, which expressed adherence to German Romantic poets' fascination with the Middle Ages and the world of German legend.
Split into simpler sentences: While he was still a student, he composed a number of ballads and published his first collection of poetry in 1898. He harked back to the German Romantic poets' fascination with the Middle Ages and the world of German legend.