Complex sentence: His second volume of poems, "Passport to the War", was published fourteen years later; the book went largely unnoticed, although it featured some of Kunitz's best-known poems, and soon fell out of print.
Split into simpler sentences: His second volume of poems, "Passport to the War", was published fourteen years later. Although it featured some of Kunitz's best-known poems, the book went largely unnoticed and soon fell out of print.