There are hundreds of stories out there of every kind about an alternate WW2 that leaves a Reich-dominated Europe up to the Urals, a massive Japanese Empire in Asia and the Pacific, and an America occupied and/or annexed and/or balkanised by the Krauts and/or Japs. Examples include Man in the High Castle, In the Presence of Mine Enemies, etc.
But whenever a realistic scenario is tryed to work out here, the concessions are huge. Japan is almost always thrown under the bus, Russia is still very much alive behind their Ural or even Brest-Litvosk borders, Germany has no colonial empire and is struggling just as hard as it can to keep the puppet states to its West and the Lebensraum to its East in line, significant amounts of the British Empire/Commonwealth are controlled by a sort of Free British exile government, America is the dominant superpower, etc., etc., etc.
MY question is, how can we realistically achieve the former scenario, and how would it play out from there. Little details can vary (i.e. whether Italy is a Great Power in its own right or just a Germany wannabe, whether India or the Americas are under German or Japanese influence, etc) but the end goal must be, with a POD no earlier than Hitler's election, and with WW2 starting of in an acceptably recognizable way (America CAN remain isolationist if need be) have the world be split between the Nazi German and Imperial Japanese camps by 1975.
Discuss.
Realistically? To invade and conquer the US by 1975? We'd have to handwave away atomic knowledge and instill Drakaverse stupidity in anyone not an Axis member. The US size, distance and relatively large population makes conquest difficult at the best and as long as the two factions are comparable in tech it's nearly impossible. Germany can be the Hyperpower, can defeat the US in a war, but actual boots on the ground is a stretch.
My thoughts on a more "Realistic" scenario:
1940:Hitler doesn't allow Goering to try and crush Dunkirk with air power alone and crushes the stranded army in the field,subsequently,with the situation looking bleak, by year ends Great Britain agrees to Hitler's generous peace terms. (Yes I know this is borderline ASB, I put Realistic in apostrophes for a reason)
1941:On the eve of what he believes will be his greatest triumph Adolf Hitler health deteriorates forcing him to step down from actual control of the country through he is still a figurehead and "spiritual adviser" to the party. (Yes I know again outlandish but considering the man's OTL health issues not nearly as ASB as before.) Due to the power struggle Hitler's departure generates, ultimately leading to a cabal leading Germany, operation Barbarossa is postponed for the immediate future. Finally Japan declares war on the US and Great Britain with Germany,near a mini civil war at home, declaring its neutrality.
1942-1943: Stalin, sensing weakness and finishing the reforms prompted from the winter war, sets out to destroy the radically anti-soviet Nazi Germany. The Anglo-American forces, distracted with Japan, pay little heed as Soviets smash through occupied Poland and drive towards German proper. The British hope both destroy each other while Americans range from complete indifference to slight support towards the Germans who are viewed as lesser evil compared to the Soviets. The war in the Pacific makes heady progress as the allies develop an island hopping campaign which skips them across towards Japan's home islands. There they vainly employ firebombing raids in hopes of breaking Japanese will.
1944:Germany, bolstered by US sold supplies and not hectored by a British navy occupied in the Pacific, stalemates the Soviet Dreadnought and eventually began to push them slowly away. During the same time an invasion of the home island occurs resulting in a high death count for all sides and leading to years of "brushfire" rebellion. FDR loses reelection, his unseemingly fourth term no less, to Thomas E. Dewey by a fraction largely attributed due to the than omni-present death figures growing larger by the day.
1945-1946:Germany continues its advances against the deteriorating Russian Hoard. The legions of veterans backed not only with increasing amounts of US arms, desperate for a market as the Pacific war slowly winded down, but advanced German weapons such as jet fighters, v-2 rockets, and assault rifles. The Soviets, ordered by Stalin to fight for every inch of worker's soil and growing desperate, "leak" information regarding the camps and atrocities being set up by the Germans in former Poland and now Russian territory in hopes of drawing the Allies into the fray. Britain, growing weary and enjoying the show, refuses while the US, retreating back into isolationism, is content to finish up with Japan and let the world be staying strictly neutral in the affair.
1947-1948-German forces take and hold Moscow along with numerous other Soviet cities. Stalin, who vowed never to give up or surrender, suffers a "health" related incident and perishes leaving Molotov free, with consent of the provisional Soviet leadership, to broker a peace deal. Germany, demanding and receiving a large pound of flesh, accepts. It continues to expand and advance its military at a worrisome rate, building larger more powerful tanks, more potent rocket-bombs and begins an expansion of its much neglected navy. Dewey, growing worried, reactivates a military project sidetracked since the end of the Pacific war. A formal defense pact between the US and Great Britain pledging to defend the other if attacked is also signed. In the '48 election Dewey eks out a bare victory trumpting his ending the hostilities in the Pacific and the peace time prosperity he helped ushered in.
1949-1952:The US stuns the world in early 1950 with the detonation of an Atomic bomb. Germany leaders most of all take note as America parades the weapon, as well as continental bomber, as the ultimate defender of liberty. They in turn found solace in their legions of jet fighters, superior to the early clumsy models either the Americans or British had, to protect their skies and their ever more powerful rocket-bombs to bomb with impunity regardless of the defenders air power. The knowledge of what Germany is doing in Eastern Europe continues to seep out and what many first assumed were typical Soviet lies grow more and more alarmed at the depraved nation. 1952 ended with the world tense, America stockpiling hundreds of atomic bombs and growing larger still, and the Soviet Remnant entering into the defense alliance with the US and British.
1953: The belief, that the A-bomb would ensure world peace, which had in part allowed Ike to secure his election was horribly challenged by Germany's first successful atomic detonation. The Furhrer wasting no time posturing the technological achievement as well as ordering a mass production of atomic warheads not for bombers but for the latest V series rocket.
1954-1955- The US countered by launching a crash program to advanced their own rocket program. By late '54 Britain, fearful for its continued existence, followed the US and Germany in detonating their own atomic bomb through they focused on building heavier bombers to make the crossing instead of rocket-bombs. Tension continues to build among the nations, each of whom keep their Atomic crews on standby.
1956- The razor-wire tight relations are snapped by a Nazi-Soviet border skirmish, A relatively common act through the years, escalates. The Nazi's quickly gain the upper hand and proceed to finish what they started the previous decade. The US issues a warning to the Furhrer that the Eisenhower doctrine will be carried through if hostilities are not halted immediately. The Furhrer, aware of America crash program resulting in an inferior but effective version of their own atomic-missile and realizing that in as little as a year the US could posses as many such rockets as his nation had accumulated in two and half years of frantic building, carries out his own prepared doctrine. U-boat commanders the world over receive their orders and launch a first strike. The counter attack, the warbirds kept at a moments notice for this eventuality, is heavier than the optimistic assurances of the Furhrer aids but facing high speed German fighter planes, backed by ground radar systems, and using simple but powerful rockets bombs instead of traditional munitions results in many, through not nearly all, of the bombers being shot down.
1957-US and Germany offically declare peace through no actual warfare had taken place for months. The two nations retreating to lick their partially self-inflicted wounds. Germany, having taken lesser damage, focuses on cannibalizing what remains of the USSR to obtain the food and raw resources its people need. The US, large segment of the government vaporized, retreats into almost anarchy through with the support of its Northern neighbor, who largely escaped damage in the war, it continues through fully removed from the world stage for the foreseeable future.
My to cents anyway.