Complex sentence: In the United States, coronation parties were mounted, one in New York City attended by the Queen's uncle and aunt, the Duke and Duchess of Windsor, while in Canada, military tattoos, horse races, parades, and fireworks displays were mounted.
Split into simpler sentences: In the United States, coronation parties were mounted, one in New York City attended by the Queen's uncle and aunt, the Duke and Duchess of Windsor. In Canada, military tattoos, horse races, parades, and fireworks displays were mounted.