Having finished the book "Five Days in London May 1940", a couple of thoughts...

First of all, it is an impressive summary of the five days during the darkest hour in Western European history, when the French armies were encircled along with the British, and Britain was facing the prospect of being alone in Europe against Germany.

One of the main strong-points and new theories for me from this book, is the following (the book's main theory of Churchill saving Europe in May 1940rests on it):

For Hitler to win his war, a war where he would dominate Europe and Western Russia, without doubts, he would have needed to fight off his three main enemies the US, UK, and Soviet Union one by one, preventing alliances from occurring, as alliances as we have later seen made the war unbearable for Hitler, even though the Soviet Union was the key in the alliance. In May of 1940, the US remained strongly neutral, and would until the end of the year, due to FDR's third election campaign, the Soviet Union was formally allied with Germany (or at peace), thus Britain was the only country left fighting and left with capacity to fight Hitler. If Britain were invaded, and destroyed in 1940, the US would not have had a role in the war, it would probably have kept itself neutral, and Hitler would have only one remaining enemy - Soviet Union. Alliances would be prevented, and how that war would have come out is beyond scope to predict, but Hitler would have been much closer to winning it, than at any point after May 1940...

When the alliance was formed, and the Soviet Union was already invaded, with the US officially in the war, Hitler could not win the war, he could only end up with a draw. He could have defeated the Soviet Union at Moscow or at Stalingrad, but he would be forced to come up with a peace settlement, as he would always be facing a thorn in the West. His empire would always be threatened by all or two powers against him in the future. Had he continued his "success" in Russia as it actually happened, and fought off a landing in 1944, he would probably have concluded a peace deal (harsh) with the Soviets, and would have been reduced to Germany.

Consequently, when Churchill made the decision to continue fighting Germany, rather than concluding a peace settlement, he knew he would be supported by the US, and that a third ally would soon appear, as an attack was imminent in the coming years (this was the information at the time; Hitler had little need for Western Europe) on the Soviet Union.

So the book argues, Hitler was as close as ever to a victory in May 1940, when Churchill had the opportunity to sue for peace. After that month, it was only a matter of a tie or a loss for Hitler. The war was won by the USSR and the Americans, but the UK did not lose it, and it did not lose it because of Churchill.

Although, in concept I agree with the above theory, the book does not give enough evidence to suggest that Churchill was ever seriously considering the peace with Hitler. He did face negotiations and opposition in the War Cabinet, but it seems Churchill coming into office was ready to keep the fight going.

Second, a similar theory can be argued basing it on yet nonexistent documents proving that Stalin was thinking of suing for peace with Hitler in the Autumn of 1941; Hitler may have accepted it, had such an approach been made. However, the document are probably hidden in the archives.

In the end, the concept that fascinates me about the 1930-1945 period, was the abundance of timepoints and single days, in which decisions were made that could turned the world we live in now upside down:

-Appeasement policy (indecision of France and UK to attack Germany after the Rhine remilitarization)
-Failure by the British to secure Norway in 1939-1940
-Molotov-Ribbentrop Pact
-May 1940
-Battle of Moscow
-Battle of Stalingrad
-D-Day

There are much more timepoints similar to the above in the course of history...