> Moreover, in a shooting war, merchant ships from other global regions attempting to supply Europe would be targeted.
This happened before, twice. The solution was convoys, it worked both times.
The convoys barely worked. Parts of Europe were desperately short of food for several years. And the non-Axis countries couldn't manage to defeat the blockade on their own: they needed help from the USA to accomplish anything.
It didn't work for Japan though. The US could've kept Japan impotent and hungry indefinitely without invading or nuking it. The main reason for nuking it was to get it to surrender before Stalin could enter the fight and take part of Japan.