All right, so Britain is out - Great Britain, free Britannica still fights on buy not much
Whatever Britain has left makes it to Newfoundland, Canada, and USA. The Bulk of the Royal Navy does not fall into German hands.
Soviets are out as well.
As Britain is invaded in and falls in 1940, USA massively starts to churn up the industry to war footing.
So US military in 1941 in the Pacific is a little better off, defenses are more. Embargo of Japan happens OTL. With Royal Navy, US does aid British Pacific bases, Royal Navy deploys more in Pacific since Europe is German bastion.
Japan strikes in 1941 maybe sooner than December, maybe with no guise of diplomacy, just a straight out attack. Similar to after France falls, Japan wants to rush in to claim Hong Kong, Singapore, the Gilberts ..... Have to attack US Pacific Fleet though to solidify.
Pearl Harbor goes down the same. Germany declares war on USA. Italy does as well.
US first response is to secure Persian oil fields and then work North to capture Russian Caspian oil fields around Baku and in Caucus. USA also supports resistance movements in USSR, Britain, France, Norway, ... occupied Europe. America is united in ridding the world of the evil Nazis and Japanese. The entire nation is behind Roosevelt.
So 1942 is a defensive fight in the Pacific and American move to secure Persian oil fields along with Kuwait and Iraq. USA targets German oil supplies, sees this as most vulnerable, on the fringe of the Nazi empire. If the USA cannot capture oil fields, they can at least put them out of action. Persia and Kuwait are first captured, Arabia is secured. Iraq is next for capture or destruction.
USA sets out to isolate Japan, Operation Starvation goes into full effect while bulk of US and Free world energy is set on defeating Germany. 1942 is defensive, ensure ANZACs are secure.
1943 - USA advances into Caucus mountains. Bomber bases are set up that can strike the eastern Med and Romanian oil fields.
USA goal is to not let Germany sit and solidify gains.
With no supplies being diverted to USSR - USA can fully dedicate to Germany. Even in WWII, USA was not 100% fully mobilized, was fighting with part of an arm ties behind the back. With a base in Persia or perhaps USA sets up base in free India, supplies flow to Persia and then to Burma .....
Canada and Australia are full in. GB is able to secure India, Pakistan, Burma after the downfall of London. Have to fight the Japanese in Burma.
Hard fight, but USA defeats Germany in 1948.
I like that North Africa, Portugal to Spain, to southern France rout as well. It will be a hard fight since Germany is not tied down as much on Eastern front.
B-17's and B-24's from Portugal then Spain and North Africa rock Germany. USA does not care about daylight precision bombing. They go for the jugular with fire bombing of industrial cities especially targeting oil facilities and fuel refineries.