Encyclopedia Americana, edition 1993, Volume 29, page 443, entry: World War II.
Author: Earl F. Zemke, Historian, Office of the Chief of Military History, Department of the Army
…April 10. On that day, the Croat troops in the Yugoslav Fourth and Seventh armies, stationed on the northern frontier, mutinied, and by nightfall both armies had been dissolved. On the afternoon of April 10, Second [German] Army troops entered Zagreb, where a newly created CROAT government WELCOMED THEM AS LIBERATORS…(!!!!!)
…In some places fighting had broken out between Croat and Serb units… (End Quote )
Encyclopedia Britannica, edition 1971, Volume 23, pages 921,922 entry: Yugoslavia, 6. WWII
(ALL verions of E.Britannica have repeated the text till at least 1986):
…The victors carved up the country. Germany and Italy divided Slovenia between them. Italy took part of Dalmatia on its own behalf and the Kosovo district and western Macedonia on behalf of Albania and set up a protectorate over Montenegro. Bulgaria annexed most of Macedonia, Hungary annexed the western half of Vojvodina (Backa) and some small districts on the Croatian border. Pavelic’ was presented by his patrons with the control of an INDEPENDENT STATE OF CROATIA; this INCLUDED ALL BOSNIA but not all Dalmatia and was nominally a kingdom, with Aimone, duke of Spoleto, second son of the duke of Aosta, as its absentee sovereign. The rump of Serbia was placed under German military occupation and was allowed from August 1941 to have a puppet government of its own under Gen. Milan Nedic. The eastern half of Vojvodina (Banat) had a separate German military administration, in which members of the local German minority played the chief part.
ARMED RESISTANCE TO THE OCCUPATION BEGAN IN BOSNIA, AND THERE THE CROATIAN FASCISTS BEGAN A MASSACRE OF SERBS WHICH, IN THE WHOLE ANNALS OF WORLD WAR II, WAS SURPASSED FOR SAVAGERY ONLY BY THE MASS EXTERMINATION OF POLISH JEWS. THE SERBS TOOK TO THE HILLS AND FORESTS TO DEFEND THEMSELVES. In Serbia itself a force led by the regular army colonel, Dragoijub (Draza) Mihajlovic (q.v.), fought Germans in the early summer. After Hitler attacked the U.S.S.R., the Yugoslav Communists, who had already made military preparations, took the field in SERBIA AND MONTENEGRO. By September  A LARGE PART of both these lands was LIBERATED by these two forces, which at first helped each other but then came to blows. In November the Germans drove all reistance forces out of Serbia and massacred thousands of people in reprisal.
(End quote )
Newly established NDH (Independent State of Croatia) simply swallowed Bosnia and Hercegovina, and northern parts of Serbia, up to Belgrade
Dr. Nora Lavin “The Holocaust” (New York, 1973).
“The streets of Belgrade were thronged with Serbs chanting “Rather war than the pact [with Hitler]”, “Rather death than slavery.” There was dancing in the squares and English and French flags were draped everywhere… The Serbs had flung their defiance at Hitler at the moment of his greatest power.The gallant little country that dared to defy Hitler was pitilessly smashed… Hitler achieved his revenge, but at a very high price. The German diversion against Yugoslavia… forced the postponement of the attack against Russia by five full weeks, a delay that would prove crucial.
William L. Shirer “The Rise and Fall of the Third Reich” (New York, 1960).
American foreign correspondent, Mr. Shirer was in Berlin and have witnessed Hitler’s outrage. “In his fury,” Shirer says “Hitler made sudden decisions which would prove utterly disastrous to the fortunes of the Third Reich.”
Variety of sources on the reaction of the world leaders
What did Churchill, Roosevelt, Hitler say about the Serbian bravery? The reaction of the Serbian spiritual leader – Patriarch Gavrilo.
MS. Ruth Mitchell “The Serbs chose war” (New York, 1943).
“In a war aimed just as much at America as at Europe, The Serbs gave us without price the three most vital months in the annals of civilization. Serbia at the end would present no bill – that I knew – because the Serbs are like that…”
THE MORAL OF THE LECTURE IN HISTORY: The proud Serbian people proved, in more than thirteen hundred years of their history, to be READY TO PAY ANY PRICE FOR THEIR FREEDOM. Freedom has no price.
There is no way Croatian fascists would fly the same Nazi flag, they used to fly during World War II, above the heads of the surviving Serbs – in lands that was for last four centuries – majority Serbian!
No one can sell to the Serbs the resurrected fascism as democracy and – (brand) “New World Order”.