Complex sentence: In 1866, the poet finished his work on "Vade-Mecum", a vast anthology of verse, which, despite his greatest efforts and formidable contacts, was unable to be published.
Split into simpler sentences: In 1866, the poet finished his work on "Vade-Mecum", a vast anthology of verse. However, despite his greatest efforts and formidable contacts, it was unable to be published.