Complex sentence: The first airsoft guns were gas-powered pistols sold in Japan in the early 1980s; originally designed for target shooting, their bullets could also hit humans without injury and they became popular for casual war-games.
Split into simpler sentences: The first airsoft guns were pistols sold in Japan in the early 1980s. Originally designed for target shooting, their bullets could also hit humans without injury and thus became popular for casual war-games.