And without a USA we would probably be living under Nazism or Communism today.Wrong. Without a single centralized polity, Germany would certainly have won... WWI. No German defeat, no Hitler. No Hitler, no Nazism. No Nazism, no WWII (not to mention, no Holocaust). No WWII, no Cold War. And if Communism had survived and remained a threat, it would have been mainly a threat to Germany.
Germany was hardly "winning" wwI when the USA entered it. This best it could have hoped for would have been a negoitiated peace the worst years more of stalemate trench warfare. OUr entry merely hastened its defeat and made it certain.