Complex sentence: At that time, the editors of "Superboy and the Legion of Super-Heroes" held periodic elections in which their audience could choose the Legion's leader; soon after his introduction, Wildfire was elected to that post.
Split into simpler sentences: At that time, the editors of "Superboy and the Legion of Super-Heroes" held periodic elections in which their audience could choose the Legion's leader. Soon after his introduction, Wildfire was elected to that post.