So an idea has been rolling around my head about what a good use could be for a British or French attack on an unaligned neutral. This would be before the US reaches wartime income. The economic penalty is large, 10 IPP up front and 8 IPP a turn until the US hits wartime income, which could result in 50, 60 or even 80+ IPPs.
The best answer that I could come up with is a British attack on Belgium on turn 1. The goal of this attack would be to stifle the Schlieffen plan and lightning war ability of Germany. With the Commonwealth being able to stack units in Belgium it would require a much larger concentration of force from Germany to destroy France which could shift the balance in the West or force Germany to turn East.
The strategy also has the positive effects of not giving Germany a ton of aligned territory when it goes to war with the UK. The USAs income also shouldn’t be able to go below zero so instead of a -8 per turn penalty it mitigates it to a -6 per turn income.
I think the largest cost is economic, delaying America and not allowing them tech rolls. Let me know what you all think and let me know if you can think of any other neutral countries that are worth invading in the early game.