>>/21672/
>>/21625/
> The Japanese would still be able to force the Siberian troops to the east, thus not letting the Germans get pushed back west initially, which would be the objective here.
Probably true, but the question of wheter or not they would precludes that of wheter or not they could. Japan wouldn't attack the USSR, not just because of their past defeats in border skirmishes but also because of the cost/benefit ratios of their two options (attacking USSR or attacking the West), as mentioned in >>/21687/.
Attacking the USSR would require a commitment to face a superior enemy on difficult terrain, with victory exclusively possible if an ally on the other side of the world succeeds, with little reward other than Vladivostok -north Asia is resource-rich but the resources are all dispersed, and as Japan couldn't count on more than limited territorial gains this means few resources could be conquered. In short: a lengthy, risky and difficult campaign for little gain.
Attacking the West allowed Japan to employ the best of its military strength against a poorly defended flank of European colonial empires, with plenty of juicy resources up for grabs. For a resource-starved Japan with an idle Navy, this was the obvious choice.
And don't forget the political struggle between Army and Navy. The Army had already gotten Japan bogged down in China and now the Navy wanted its turn.
> thus they accept the peace offers with both Germany and Italy
Getting Britain out of the war would be even bigger than that. The Acchiles Heel of Germany's economy in both World Wars was the crippling naval blockade cutting off its access to key imported raw materials, and global trade in general. Lift the blockade and Gitler gets a monumental economic boost.
But it's also easier said than done. There were military reasons for the failure to annihilate the Britons in Dunkirk, so an all-out attempt to destroy the retreating defeat could be harmful to the remainder of the French campaign or just fail. And even success at Dunkirk wouldn't guarantee a British exit from the war; Hitler repeatedly underestimated Britain's will to wage war and take it to its very last consequences.