Complex sentence: A new resurgence of masquerade balls began in the late 1990s in North America and are still held today, though in modern times the party atmosphere is emphasized and the formal dancing usually less prominent.
Split into simpler sentences: A new resurgence of masquerade balls began in the late 1990s in North America. They still take place today, though in modern times the party atmosphere is emphasized and the formal dancing usually less prominent.