 The SAO Krajina, renamed Republic of Serbian Krajina (RSK) on 19 December 1991, responded with a campaign of ethnic cleansing against Croatian civilians.With the Yugoslav People's Army (JNA) lending support to SAO Krajina leadership and the Croatian Police unable to cope with the situation, the Croatian National Guard (ZNG) was formed in May 1991.The development of the military of Croatia was hampered by a UN arms embargo introduced in September, while the military conflict in Croatia continued to escalate.