That sounds a bit wankish for the allies - but is something I could live with
. Not sure how, given a war in the Pacific ongoing, the US would get in that much earlier, especially if Britain is neutral. If Britain and France both declared war, even if they did relatively little militarily, that would give a basis for a US dow when Poland is attacked.
In terms of the suggested Pacific war both sides would be significantly weaker with less ships in service and development of areas, most especially carrier warfare. Presuming no other power gets involved it could be a tough struggle for the US. Japan will be able to concentrate it's strength against the US and possibly get the battle it wants in the region of the Philippines. Also it's not as deep into China and so will be less bogged down there. Will-power permitting the US will win in the end but there could be some heavy fighting and can't see it being resolved by nukes. Also, presuming no Soviet intervention it would probably require a bloody invasion of Japan.
That would fit in with the 6 year OP duration for a Pacific war. If Britain also got involved, for whatever reason, the war should be shorter as more resources to throw into the mix and Malaya will be a lot safer with the Japanese not in a position to attack it, plus possibly both western powers intervening on the Chinese mainland.
Presuming this doesn't butterfly the European war, unlikely but possible I suppose, then in the short term it could handicap the western powers. With America tooling up for war there won't be the spare capacity in US industries, so the investment Britain and France supplied OTL will have to go, at a somewhat slower rate, into their own industries. Possibly some economic boost because America and Japan are less competition economically and the fact of war should help loosen the purse strings a bit in the allies powers, although whether those extra funds would be used efficiently would be an interesting question.
If Britain joins this early Pacific war it will mean losses and diversion of forces reducing it's impact in Europe. However it will also mean battle experience for some troops and an higher rate of production while the homeland is still at peace and secure - i.e. not impeded by blockade or blackout for instance. [Less certain about France getting involved but a similar effect if they do although, with a land border with Germany their likely to commit very little to the east, although base access and some light naval units would be useful as would diplomatic/economic support].
However, presuming there is a European conflict and the US joins it earlier then an even partially tooled up US would have a huge difference. Especially if possibly in time to prevent a collapse of France although probably unlikely if the Ardennes attack still occurs. [Although without a number of butterflies unrelated to American military status the Germans could still come a nasty cropper there
]. One oddity might be if the Pacific war triggers Britain and France, whether with or without US support, decides to stand up to Germany over the Sudatenland. Also, if their facing no threat from Japan how will Russia react to circumstances in Europe?
For my own guess about the significance of the extra 30'. Either - forget it I see loughery111 has answered the point and I was way off.
Steve
