Complex sentence: It featured a fast, intense drumbeat which Discharge would later emulate with distinctive D-beat starting 1979 before changing their line-up and beginning a new style indebted to heavy metal.
Split into simpler sentences: It featured a fast, intense drumbeat which Discharge would later emulate with distinctive D-beat starting 1979. Also In 1979, the group Discharge changed its line-up and began a new style indebted to heavy metal.