Complex sentence: The 2009 "Summer of Chillwave" was marked by an inundation of artists writing and performing songs about the beach and summertime with its vanguard represented by the trinity of Neon Indian, Washed Out, and Toro y Moi.
Split into simpler sentences: The 2009 "Summer of Chillwave" was marked by an inundation of artists writing and performing songs about the beach and summertime. The vanguard was represented by the trinity of Neon Indian, Washed Out, and Toro y Moi.