One month after Croatia declared its independence, the Yugoslav army and other Serb forces held something less than one-third of the Croatian territory, mostly in areas with a predominantly ethnic Serb population. The JNA military strategy partly consisted of extensive shelling, at times irrespective of the presence of civilians. As the war progressed, the cities of Dubrovnik, Gospić, Šibenik, Zadar, Karlovac, Sisak, Slavonski Brod, Osijek, Vinkovci, and Vukovar all came under attack by Yugoslav forces. The United Nations (UN) imposed a weapons embargo; this did not affect JNA-backed Serb forces significantly, as they had the JNA arsenal at their disposal, but it caused serious trouble for the newly formed Croatian army. The Croatian government started smuggling weapons over its borders.