If anything, the war in Yugoslavia was a continuation of events of the collapse of the Ottoman Empire and the attempt by Russia to gain Meditteranean access so you could make a case for the Russo-Turkish war of 1878.
History in this region does not divide up into neat parcels of activity, events from generations before had some effect on creating the 1878 war, but many historians would probably go for the Balkan wars of 1912-13.
On the whole Normandy Campaign, from 6th of June, to 1st of August, the British forces suffered per division more casualties than any other campaign in their history, including the Somme. Something like 4000 AFVs were lost in the battles for caen alone.
He certainly was full of public bluster, but the Willy-Nicky correspondence, and his reaction to the Austro-Hungarian ultimatum tend to show otherwise.
The only plausible change I can see in history to make WWI end more quickly and less bloodily is the Germans beat France in 1914, say by a/ sticking to the Schlieffen Plan b/ continuing to Paris, not trying to surround the French armies in the south, and c/ not withdrawing two corps from the advance on Paris to the Russian front at a crucial moment.
Given that, there’s a huge change in European history in the c20th; essentially Germany achieves its aim of domination over Europe, keeps Alsace and Lorraine, the Russian revolution probably never happens, the US, Italy and Turkey don’t join the war … the further consequences of all these changes are pretty much unimaginable.
If you mean, had the Eastern Front been quiet at the time: no it wouldn’t have. Overlord had a couple of months of hard fighting but the outcome was never in doubt. Another couple of German divisions perhaps would make no huge difference to that.
If you mean, had there been no war in Russia: well yes but then it’s not really WWII any more. Hitler was always going to attack Russia.
Nope. They take a little longer and don’t need to stop before the Rhine, but the Russians will beat the Germans single-handed almost no matter what plausible change you make in history.