the US had to intervene because just as England did during 4 centuries, they had to prevent a united Europe frome arising.
By united I of course do not mean controlled by a single country form Gibraltar to Istanbul, but a Europe where a single country would have reached a level of power sufficient for all the other countries to be considered as vassals or satellites.
I am quite convinced that the US share The insularian mentality of the UK, and therefore consider or at least did consider that their security requires a Europe sufficiently divided. Had Germany won the WWI, it would have become the unique powerhouse of the continent, possibly grabbing large chunks of the French and British colonial empires in the process.
Beyond the fight against nazism and communism lies the same concern, united Europe weither nazi, kaiserist or communist would have been an unacceptable risk for US security.
Hear me here, I am not saying the US wants Europe to be divided, but it cannot accept it to be united or controlled by a power whose policy appears aggressive towards the US. Germany at that time was an aggressive country because it wanted to modify colonial spoil-sharing example : what they did in Morocco in 1905 and 1911, furthermore they wanted to become a global power, shown by their fleet development policy.
Being in control of Europe germany could have clashed with the US in many areas of the world, South America of course but Pacific ocean islands as well ( bismarck islands ).
Once the US perceived Germany as being the country with the most aggressive stance, it had to oppose them. Furthermore, the US allied a coalition of France and GB, making sure that it did not create a monster after the war by giving to much power to a single country. That it also why they were very suspicious towards France in the twenties, fearing it might try to establish itself as the central power in Europe.