Complex sentence: The 2004 Istanbul summit was held in Istanbul, Turkey from June 28 to June 29,2004; and was the 17th NATO summit in which NATO's Heads of State and Governments met to make formal decisions about security topics.
Split into simpler sentences: The 2004 Istanbul summit was held in Istanbul, Turkey from June 28 to June 29,2004. It was the 17th NATO summit in which NATO's Heads of State and Governments met to make formal decisions about security topics.