What if Eisenhower Had Postponed the D-Day Landings? (Okay, it has been done before, but there may still be a few nuggets to be mined here.)
There would have been intense pressure to go at the next moment the moon and the tides were right. That would have put the landing around June 18, just in time for the severe storm. That storm, by the way, came up without warning, which is part of the reason it did the damage it did. If the allies had been caught by the storm in the early stages of the landing, with troops trying to establish themselves on the beaches, the troops that made it would have been cut off from resupply and reinforcements for almost four days. Allied air power would have been neutralized. The Germans might well have been able to destroy the invasion on the beaches and destroy airborne forces before they could link up with the main invasion force.
Immediate results: The initial invasion force essentially wiped out--well over 100,000 men killed or captured, including a lot of specialists like the airborne troops. Lots of equipment captured or destroyed, including landing craft, specialized tanks, and other vital cogs in the allied wheel. The artificial harbors that made supply over the beaches at Normandy possible would have been destroyed by the storm on their way over. Bottom line: An allied disaster that would make an immediate second try very unlikely.
Short-term results(Thru August): As the magnitude of the German victory became apparent, German allies like Romania who were edging away may well have decided to wait a while longer. The French Resistance would have probably been decimated. It would have made a supreme effort at the time of the landing, but the Germans would have been free to throw as much at the French as they needed to with the threat of invasion temporarily lifted. If the Russians still launched the ambitious attack that in the real world destroyed Army Group Center, they probably would not have been anywhere near as successful, because the Germans could have brought in reinforcements from the west. The Soviets would have still gained territory and inflicted severe losses, but the campaign probably wouldn't have been decisive. The allies would have still made progress in Italy, but I would guess that the landings in Southern France would have been postponed. So, by the end of August, instead of the war in Europe being essentially won, it would still be an iffy thing.
The western allies would still have the military power to try a second invasion of France, but would they use it? England would be pushing the Americans to concentrate on Italy and the Balkans, using the threat of a second attempt at France as a means of pinning down Germans, while the real action happened elsewhere. The Americans would want to make another try in France, but political factors might intervene. Roosevelt would be politically weakened by the disaster with an election coming up. The American navy would be encouraged to push for a Japan-first strategy. Roosevelt might go for that as a political necessity after the D-Day disaster. He would certainly be very reluctant to push for another risky invasion with the election approaching. The Soviets would howl because their promised second front didn't happen. The western allies might decide to use the forces and landing craft allocated to the invasion of southern France to speed up progress in Italy. Capturing Rome would take some of the sting out of the D-Day disaster. Victories in the Pacific would also help.
Consequences Through 1945: This gets a little more iffy. The Allies still have an overwhelming advantage in production and manpower. The Germans are still handicapped by the fact that Hitler is leading them. On the other hand, Germany had technical superiority in tanks and aircraft, and the Speer industry mobilization would have more resources to work with. Keeping France would help German air defenses over Germany by giving more warning and forcing allies to fly longer distances. Those factors would allow German production to rise even more than it actually did in late 1944 and early 1945. Producing vast numbers of conventional aircraft and Sherman tanks with 75mm guns wouldn't help the allies as much as the numbers would suggest if those aircraft were going up against a couple thousand ME262s and those tanks had to face Panthers and Tigers.
The real Normandy invasion made the army face up to problems with the Sherman, and forced rapid improvements, as well as production of the Pershing. Encounters with Panthers and Tigers in Italy hadn't done that. They might eventually have in this scenario, or survivors of the Normandy invasion could have brought back stories of Shermans unable to penetrate Panthers at any range. That could have shaken the army out of it's complacency. If it didn't, a good part of allied tank production would be close to obsolete by 1945.
I don't know what the allies would do. I can't see the English going along with another cross channel invasion in late 1944 or early 1945. I can't see the United States giving up that idea. Italy would be a long hard climb. The Balkans also had limited potential. In the absence of a strong Western front, I suspect that the Soviet Army would have made some gains, but they would have been slower and much more costly than they were historically. Soviet losses in the war were historically incredibly high. If the Germans were able to shift divisions east, the Soviets would have had an even tougher time. Another year of relatively even fighting would have made losses even higher. At some point even the Soviets might have been forced to gear down a bit. They might have even sought a separate peace, though that would have been difficult for even Stalin to pull off given the level of hatred the Nazi had managed to induce.
The End Of The War: In any case, the war would almost certainly still end in August or September 1945, with the US dropping atom bombs on Germany. That would probably be followed in fairly short order by the German military deposing Hitler and suing for peace. Hopefully they wouldn't be stupid enough to try to fight it out. The peace that resulted would have been far different though.
What if the German army still controlled most or all of Germany, and part or all of France and the Balkans when the bombs dropped? Things could get incredibly ugly.
--> Communist and anti-Communist forces would rush to "liberate" territory in the Balkans and France.
--> The Soviets would scramble to grab as much as they could in the east.
--> The Polish home army would undoubtedly try to seize Warsaw and other key Polish cities
before the Soviets got there.
--> Soviet citizens serving in the German army would fight very hard to avoid being sent back to
Russia, as would a lot of the slave laborers.
--> Die-hard Nazis would yell "stab in the back" and start trying to take back the government.
--> Laborers from every country in Europe would be milling around, and/or fighting.
--> Ukrainians would start fighting Poles for any Ukrainian-language territory that was still in
German hands.
--> The Yugoslavs would have a three or more cornered war between Croatian nationalists,
Serbian nationalists, and Communists.
With the Germans undefeated until August 1945, the Soviets would not have been able to shift massive amounts of troops to attack Manchuria. They would have probably still tried to grab some territory as soon as the bombs dropped, but without 3 or 4 months of preparations, the results would not have been as spectacular. American reaction would not have been as kind either. With Communists fighting for power in several European countries, the United States would undoubtedly see a Manchurian attack as contemptible.
Unless the allies had already settled who would control what after the war before the bombs dropped, this could get incredibly ugly.
-->The Germans would want to surrender to the Western Allies, but the Soviets would want some
fruits from their efforts.
--> German and Japanese military equipment would be a prize to be seized by a bewildering array
of small countries and would-be countries.
--> Surrendering Germans could set the balance of power between Hungary and Romania,
between Hungary and Slovakia.
--> Just about every territorial dispute in eastern and Central Europe would be reopened.
--> The Nationalist and Communist Chinese would race to take surrenders of Japanese military
and the part of Manchuria that was not in Soviet hands.
--> The chances for clashes between the Soviets and a non-communist Poland over border regions
would be very high.
The western allies would have to make a lot of very tough choices in a very short time. Would they be able to make a real peace, or would World War II against the Nazis quickly merge into a second round between the west and the Soviets? What kind of world would emerge? My guess is that it would be a fun place to write about, but I wouldn't want to live there. If you have any thoughts on the scenario, e-mail me.