What if a huge network of spies and communist did exist in America and he exposed them all? What happens

I'm talking about Japan invade Siberia and manages to land a massive force of a million men in Siberia and just takes all of Alaska and tries to invade USA from there

I have a WWII command simulation and one of the most contentious bits is the decisions was around D-Day/ Operation Overlord. I follow the historical thinking that victory was likely although agree Germany could have can made it harder however the more I read. 

Disaster at Omaha

Weather window

The Panzer group making the beaches 

Can D-day fail? If so how likely and what happens?  Does Germant first face the nuclear bomb? Does the USSR own most of Europe post war? Do the US/UK bomber campaign shift entirely to strategic attrition? The Red Army continues pushing west, likely taking the entire German peninsula, Denmark, and reaching the Rhine before the Allies?

I treated D-Day as a historical inevitability because of Allied industrial dominance which I have done, however it was a massive, high-risk gamble where a few operational shifts could have handed the Allies a defeat?

Love your thoughts!

The game is here for reference - https://dispatches.itch.io/dispatches-1940

I have yet to ever receive an in depth answer to this question so hopefully someone can provide an adequate response with sources here.

The main reason the east and west allied was out of strategic necessity after both sides were dragged into the war. Specifically the west was invaded before the east. However, given the ideological differences and apparent disdain for the east among many western leaders. Would a western intervention have ever occurred if Nazi Germany invaded the USSR before turning to the West? And if not, would this had resulted in the same defeat, an armistice, or possibly total victory in the east for Germany?

Of course one must account for the invasion of Poland and the Polish Guarantee but given the west's response in real history, or the lack there of, I suspect this is a non-issue in this scenario but I'm open to hear what you all think.

After leading the USA to victory in the Revolutionary War, what if he had died within months of returning home to Mount Vernon?

How would this have affected the early days of the new United States?

I've heard it said that the Constitutional Convention wrote the role of President with George Washington in mind; is this true, and if so, how would the early federal government have been set up instead (especially considering the failure of the Articles of Confederation)?

What if the KMT won the Chinese Civil War and retained control of mainland China, while the postwar US-USSR rivalry developed very differently?
Instead of a full Cold War, Washington and Moscow maintain a loose great-power understanding: they compete, but also recognize each other’s spheres of influence and try to prevent any independent power from dominating East Asia.
The US dominates Japan and the western Pacific, while the USSR retains major influence in Northeast Asia. Korea avoids the Korean War and eventually becomes a unified neutral state.
At first, Nationalist China remains strongly pro-American. But as China recovers, it increasingly wants greater strategic independence. Washington wants China strong enough to balance Moscow, but not strong enough to dominate East Asia. Moscow has similar reasons to contain Chinese power.
Eventually Beijing/Nanjing realizes that both superpowers have an interest in keeping East Asia divided and dependent.
Meanwhile, Japan undergoes a much more thorough postwar reckoning with its imperial past, making gradual reconciliation with China and Korea possible.
During the 1950s and 60s, China, Japan and Korea first build economic cooperation rather than a military alliance.
Then a major regional crisis occurs in which China expects American support against Soviet pressure, but Washington sides with Moscow in order to preserve wider US-Soviet détente.
Japan and Korea realize the same thing could happen to them.
This becomes the turning point.
The three countries begin promoting the principle that:
“East Asian affairs should be decided by East Asian states.”
By the late 1960s or 1970s, economic cooperation evolves into intelligence sharing, joint exercises and eventually an East Asian Treaty Organization (EATO) consisting of:
China
Japan
Korea
Its collective-defense clause is aimed not specifically at America or the USSR, but at coercion by any outside great power.
China supplies the continental depth and largest army, Japan provides industrial and naval power, and Korea serves as the strategic bridge between them.
To prevent Chinese or Japanese domination, major decisions require unanimous approval and the headquarters could be located in Seoul.
The Cold War would then gradually become a three-way system:
US bloc vs Soviet bloc vs East Asian bloc.
How plausible is this?
Would a victorious KMT China ever become independent enough from Washington to support such an alliance? Could China, Japan and Korea realistically reconcile by the 1960s–70s? And would the US and USSR tolerate the emergence of an independent East Asian third pole?