Harry Turtledove's Hitler's War

Lector

Hi, I've just finished Hitler's War by Harry Turtledove. It's an alternative, what-if history of WWII, with the major difference being that war breaks out over Czechoslovakia in 1938, rather than over Poland in 1939. Individual parts of the book were OK and reasonably well written, but there was no attempt to give a big picture.
A more serious problem I had with the book concerns the subsequent divergence from history. War over Czechoslovakia is plausible, but why would Stalin have so enthusiastically joined in? A year later (in real time), the Nazi-Soviet non-aggression pact was signed, and Stalin refused to react to Hitler's aggression until the 1941 invasion. But in this alternative, he throws men and materiel into the defence of Czechoslovakia, and then invades Poland. Why? We aren't given any reasons. Also, the Japanese invade (rather, at the end of the book, they were preparing to invade) Siberia, and capture Vladivostok. Again, no reason is given for this divergence, other than hints at Soviet involvement in the west. In real time, when the Soviets were staring defeat in the face (1941-1942), the Japanese chose to capture South-East Asia.
A lot of the problems may stem from Turtledove's reliance on the "little guy" for his POV. No big names make it to his list of characters - Hitler and Chamberlain just flicking in and out of the early chapters.
In summary, this book has an interesting premise, but goes off the boil quickly.
Anybody got any other opinions on this book?

Reekwind

I'm not a Turtledove fan (not since his Southern Victory years at least) and I've not read this particular work but a few notes:

1) The Soviet Union was at the forefront of the 'collective security' push to shackle Germany in the 1930s. Moscow announced its readiness to go to war over Czechoslovakia in 1938 (how far it would have actually gone was never tested) as per its various treaty obligations. Hence much of the shock of the 1939 Nazi-Soviet NAP - it was a complete reversal of the previous Soviet position

2) The Japanese did historically invade Siberia, as part of the border skirmishes in 1939. These weren't ended until the Red Army crushed the Japanese at Khalkhin Gol in September of that year. This tilted the power in Tokyo towards the Navy who advocated a push into SE Asia and a confrontation with the US. What does seem ahistorical is the idea that the Imperial Army could take Vladivostok, either through force of arms or because Stalin had neglected the Far East

Manach

Not read this series by him, though usually his work is middling to good. I'd recommend his one-off novel where the Spanish Armada succeed in 1588, 'Ruled Britannia', with a certain Bill Shakespeare taking a central role.