Complex sentence: Such songs about important events were sometimes being sung very soon after the military events described; the Spanish "Cantar de Mio Cid" shows that a comparable narrative tradition existed in Spain at the same period.
Split into simpler sentences: Such songs about important events were sometimes being sung very soon after the military events described. The Spanish "Cantar de Mio Cid" shows that a comparable narrative tradition existed in Spain at the same period.