Complex sentence: Leopold was evidently unaware of the negative light in which he was generally viewed; he did, however, perceive that there was some intangible barrier to his Italian ambitions, and eventually recognised that he could not overcome whatever forces were arrayed against him.
Split into simpler sentences: Leopold was evidently unaware of the negative light in which he was generally viewed. Ignorant of the truth, Leopold could nevertheless perceive a barrier to his Italian hopes, and eventually recognised that he could not overcome the forces arrayed against him.