In May, the Croatian government responded by forming the Croatian National Guard ("Zbor narodne garde" - ZNG), but its development was hampered by a United Nations (UN) arms embargo introduced in September. On 8 October, Croatia declared independence from Yugoslavia, and a month later the ZNG was renamed the Croatian Army ("Hrvatska vojska" - HV). Late 1991 saw the fiercest fighting of the war, as the Yugoslav campaign in Croatia culminated in the Siege of Dubrovnik, and the Battle of Vukovar.