Delta Force
Banned
Weren't the British the worlds largest international investors prior to WW1? I also believe they already pumped a lot of money into funding the other Allies, chiefly France. I would think they could be able to generate a lot more liquidity than Germany or the other Central Powers if they were forced to.
London was the center of international finance in the early 1900s. The British Pound was the world reserve currency, like the United States Dollar after World War II. The British could call on the Dominions to help finance the war as well.
There are two issues - one is trade, the other finance. In a sense for at least the first couple of years of the war the US was neutral with respect to trade, the realities of the military situation was that except for a couple of voyages of a merchant sub nothing could get to Germany. However the US did not protest too much the RN blockade of Germany which included everything with food, medical supplies, etc not being allowed which was contrary to accepted practice for distant, as opposed to close, blockade. The key deal was finance. rather rapidly a good deal of the Entente purchases from the US from food to ammunition were made with loans made by US financiers to the Entente nations, subsequently backed by the US government after the US entered the war (an expectation of many of the loaners). Some money was loaned to the Central Powers but not so much. The Entente powers would have had a great deal of difficulty paying for the purchases absent the loans, running down gold reserves to next to nothing and probably incurring significant inflation.
So...no loans to either side will hurt the Entente way more than the Central Powers, and if the USA tells the UK and France that if they don't allow at least "humanitarian" trade with CP, no war related material will be sold to them...
The United States has always advocated freedom of the seas, so I don't know where you would get the impression that the Royal Navy blockade wasn't an issue, because it was.