A second American civil war during the First World War

How would an American civil war beginning in 1916 affect the First World War?

It would weaken Allied supply and manpower and reshape convoy operations, but Germany might still collapse under blockade by 1918-19.

The Allies would lose American troops, destroyers, and much export capacity, while Canada faced border security and refugees. Japan might supply more destroyers and perhaps other forces to compensate for the missing American contribution. The blockade would still starve and destabilize Germany, so an Allied victory around 1918-19 remains plausible. The duration and technological effects of the American conflict would depend heavily on which industrial regions joined each side.