Complex sentence: More than 70 million visitors from not only Ansan but also all over the country gathered to see the 4th international performance opened in 2008, it was a great opportunity to grow into national festival.
Split into simpler sentences: More than 70 million visitors from not only Ansan but also all over the country gathered to see the 4th international performance. And when it opened in 2008, it was a great opportunity to grow into a national festival.