Complex sentence: When this topic turned out not to be feasible, he switched to studying the question of Italian unification over a two-year period, which resulted in his first book, "The Italian Problem in European Diplomacy, 1847--49" published in 1934.
Split into simpler sentences: When this topic turned out not to be feasible, he switched to studying the question of Italian unification over a two-year period. This resulted in his first book, "The Italian Problem in European Diplomacy, 1847--49" published in 1934.