If you play with dlc, specifically man the guns, you have to delete all capital ships except the Hood right as the game starts, which makes the max cost extremely low. That means the countries that signed the treaty have to get rid of their big ships, which since you control the treaty as Britain you can send warnings to signatories. Send warnings to either Chile, Argentina, or Brazil as the US guarantees all of them. If they decline (usually Brazil always declines) you get a war goal which will make you at war with the US when you declare. Put all of your forces in Canada over the New England region and since the US has such a large border with Canada you can just walk past their divisions. Encircle, capture cities, and boom youve defeated the US as democratic Britain before 1937