Complex sentence: They were one of the pioneers of rock and roll in The Netherlands and band became famous in Europe playing a kind of rock and roll later called Indorock, a fusion of Indonesian and Western music with its roots in Kroncong.
Split into simpler sentences: They were one of the pioneers of rock and roll in The Netherlands. Their music was later called Indorock, a fusion of Indonesian and Western music, and has roots in Kroncong.