Complex sentence: The first SwarmFest was in 1998 and were held sponsored by the Santa Fe Institute, after the SDG was formed in late 1999, from 2000 onwards SwarmFests were organized directly by the SDG.
Split into simpler sentences: The first SwarmFest was in 1998 while Swarm was still sponsored by the Santa Fe Institute, after the SDG was formed in late 1999. From SwarmFest 2000 onwards, SwarmFests were organized directly by the SDG.