That America withdrew from the world so soon after WW1 had a profound effect on Europe’s ability to keep the peace.
It meant that the Anglo-American guarantee was worthless before it had even got going, and the French had agreed to compromise on the Treaty of Versailles only because America and Britain had guaranteed to come to its aid should Germany attack it again.
It left Britain and France as the leading nations in the League of Nations and, weakened as they were, it meant that the League, too, was weakened.
It meant that Britain and France were as worried about the Bolshevik revolution in Russia as they were with fascism in Italy or the rise to power of the Nazis in Germany. They could only defend themselves against one of them, but which carried the greater threat?
Whilst they both also had their empires to worry about.
We see the results of all of this in the Manchuria crisis, in the Hoare-Laval Pact and Abyssinia, in Appeasement right up to Munich, and in their reluctance to reach a deal with Stalin.