Complex sentence: As the Yugoslav People's Army (JNA) increasingly supported the SAO Krajina and the Croatian Police was unable to cope with the situation, the Croatian National Guard (ZNG) was formed in May 1991.
Split into simpler sentences: As the Yugoslav People's Army (JNA) increasingly supported the SAO Krajina, the Croatian Police were unable to cope. Thus, the Croatian National Guard (ZNG) was formed in May 1991.