In OTL, one of the biggest things that made the USA join the Allies in WW1 was Germany's policy of attacking neutral shipping. What if Germany, early in the war, doesn't adopt this policy, but the UK does? This probably needs to go a bit more further back to work, such as increased animosity between the USA/UK in the late nineteenth and early twentieth centuries. What could lead to the UK adopting such a policy, and what are it's effects?