One thing with geopolitics between 1870 and 1910 is that North America was a pretty stable place. No civil wars and loans were repaid. So North America wasn't a pre-occupation of European diplomats nor presented a flashpoint for the crisis. OTOH, when Mexico couldn't repay its debts and there were civil wars in both Mexico and the USA, Europeans did intervene militarily in Mexico and also the American Civil War produced a major diplomatic crisis in the Trent Affair.
So yes, if North America becomes a lot less stable as a result of the events leading to a successful Confederate succession, which is pretty much everything except for it occurring peacefully, then North America becomes a sphere for geopolitics and this starts affecting alliances in Europe. Its no different in this respect from Africa, China, or the Ottoman Empire and OTL it wae the Ottoman Empire and its successor states that provided the flashpoint for the Great War.
So yes, if North America becomes a lot less stable as a result of the events leading to a successful Confederate succession, which is pretty much everything except for it occurring peacefully, then North America becomes a sphere for geopolitics and this starts affecting alliances in Europe. Its no different in this respect from Africa, China, or the Ottoman Empire and OTL it wae the Ottoman Empire and its successor states that provided the flashpoint for the Great War.