As stated above the easiest way to do this is eliminate FDR. Maybe have him not run in 1940 following the tradition of only 2 terms per president or have him die of an earlier illness.
If historic events then proceed rather similar to our timeline with no US entry and probably no attack on pearl harbor you'll have a stalemate in North Africa and a stalemate on the Eastern front by 42-3.
Eventually something will have to give. I imagine England will break first, there is only so long the English people are going to endure bombings with nothing to show for it. Peace feelers will be sent out for a peace with honor. England isn't going to surrender they just want to stop fighting.
What this peace will look like can go 1 of 2 ways: Either back to a status quo pre war. England withdraws to its borders, gives back Italian East Africa and any gains it made in North Africa, though in this situation where they are giving back land, I would assume England is losing in North Africa and the Germans and Italians are somewhere in Egypt. The English would rather hold on to Egypt than Ethiopia.
Or, current borders stand. This is more likely in the scenario where England made significant gains in Libya but just doesn't have the will to fight anymore. Mussolini will rage, but Hitler is going to call the shots here. Mussolini will probably be placated by extra land in Yugoslavia or being allowed to take Tunisia, Corsica and maybe parts of Vichy France. No one is going to stand up for Vichy and they'll be forced to go along.
Now, if the OP requires there be Japanese and US intervention what we can have is the following:
1. Have Stalingrad fall. Stalin gets a major hit to his prestige, but the Germans don't really gain much. The city is in ruins and rather useless to them and the offensive bogs down somewhere east of the city. Germany has more troops and higher morale, but still not enough to crush the Russians whereas the Russians have lost a major transit hub and several factories. The Soviet Union is weakened but not out of the fight.
2. North African campaign goes as it did in OTL. But, this time Germany manages to evacuate more troops out of North Africa into Italy.
3. Now, we need to find a reason for the invasion of Italy not to happen to infuriate Stalin. There are several ways this can be done:
a. The Americans force the British's hand and declares they want to only attack France, no distractions. British are forced to accept but work to delay the invasion an extra year and not opening another front.
b. Similar to above. But, this time they come to the conclusion together that Italy is not a threat and will be a waste of resources and will just result in bogged down Alpine fighting. Maybe there is an invasion of Sardinia to use a spring board for Southern France. No D-Day until 44.
c. The Western Allies agree that Stalin is going to be a future threat and should come out of this war as weak as possible. This can either be done by listening to elements within the government that were already extremely anti communist or the allies discover just how heavily entrenched Soviet spy rings are in the United States and Britain. Let the Soviets bleed themselves white against the Germans.
4. Throughout 43 and into 44 Stalin is furious. His soldiers are being killed by the hundreds of thousands while America and Britain just sit and prepare for an "upcoming invasion." The Germans are pushed backed and Stalingrad is reclaimed, but he is facing hundreds of thousands of additional German soldiers. He has reclaimed much of his land, but doesn't think his forces can push on much further and sends out feelers to Hitler.
5. Hitler at first is adamant that nothing short of total victory will be accepted, but his generals as well as members of his inner circle(including Speer, Himmler and Goebbels) see that the war is going to leave Germany in ruins if they continue. After several weeks of debate they manage to convince Hitler to accept a Brest-Litvosk type peace. They call it a temporary cease fire "Let us breath, establish infrastructure, rebuild our forces and we can resume the war in a few years after we get the United States and Britain out."
6. In early 1944, peace is called on the Eastern front. Germany and its allies consolidate their gains as dozens of divisions race west to shore up the defenses in France. Britain and the United States both realize their assessments for troop numbers in the west now are completely useless and that the invasion is in jeopardy. They gambled that Stalin would fight to the last man and they gambled wrong.
7. Peace envoys are sent to Germany to discuss a treaty. This may result in Germany leaving France and the low countries while keeping Denmark and Norway(I think the Germans will insist on having some atlantic ports). The Free French government won't return, but Vichy will now control all of France. Italy will lose its colonies and Mussolini's power will be greatly diminished.
As for Japan: I really can't fathom a way Japan survive if Pearl Harbor takes place the way it does. Perhaps if the Japanese actually declare war prior to the attack and suffer a major defeat at Pearl Harbor there may be room for a negotiated settlement. Or, if the attack on Pearl Harbor never takes place and they commit to a more limited war by just attacking the Philippines. The United States will retake the Philippines, probably take some other Japanese held islands and then call it quits.
