An American entry on Germany's side would transform both world wars

How would World War II develop if the United States had entered World War I on Germany's side and later returned to neutrality?

The first war would change so much that Canada, Russia, naval treaties, and U.S. party politics would all reshape the path to any second war.

American alignment with Germany would first remake the end of World War I, so there is no simple path to a familiar World War II. Canada and Russia could emerge in very different forms, and the naval treaty settlement might never exist. Domestic American politics could reverse the alliance after an election and bring a successor administration back toward Britain. An effort to repair the earlier rupture could even cause the United States to enter a later war sooner rather than remain neutral.