Complex sentence: Culture of Peace & Nonviolence for the Children of the World which would be ushered in by "One Day of Peace," and in November 1999, the U.N. issued a formal invitation for world participation.
Split into simpler sentences: Culture of Peace & Nonviolence for the Children of the World which would be ushered in by "One Day of Peace." Finally, in November 1999, the U.N. issued a formal invitation for world participation.