Complex sentence: However, the terms of Villafranca were never to come into effect: although they were reaffirmed by the final Treaty of Zürich in November, by then the agreement had become a dead letter.
Split into simpler sentences: However, the terms of Villafranca were never to come into effect. Although they were reaffirmed by the final Treaty of Zürich in November, by then the agreement had become a dead letter.