Would the US entering the war have changed the Versailles agreement, which was famously lenient? Germany got to retain Poland and Lithuania and simply had to return Alsace-Lorraine to France. Austria-Hungary had to withdraw from Bosnia and Trieste, and the Ottomans ceded Palestine to Britain. Relatively minor stuff, really
Yes it would've. The Versailles agreement was leninent because both parties pretty much beat each other down the ground with no clear winner. The Entente won by the skin of their teeth. US involvement would mean a firmer vicotry and maybe the Entente becoming more demanding in their stuff. Would lead to a lot more bitter feelings which could lead to future problems (kinda like the inanity of the Spanish Civil War and Portuguese Civil War. Both fell to autocracies for years until thehy were overthrown when Russia convinced the others to fund the socialist resistance.)
Look at all that would not have happened.
The Ottomans would struggle financially though they cut a deal with the US to help deal with financial troubles and they would eventually find the huge oil deposits in their area. Ottomans become a great power once more with the petrol going toward their German (and later Austrian) ally and the Americans. Even if Ottomans didn't hold a grudge for Palestine, they would still be mad at the British trying to back up the Sauds for rebellion in the Rishidi-Saud War (which, despite British efforts, the Rishidi won thanks to Ottoman supprot and the Germans "accidentally" leaving military equipment for the Ottomans to give) and a union between the Houses of Osman and Rishid was born from it. Ottoman-Arabian Empire was a large stabilizing force for the various post-colonial Muslim states, especially in North Africa. A more wrathful Versailes agreement would probably cause the uprising of the Turk nationalists and destabilize the Middle East, especially since the British and French would tyr and carve it up.
Granted, the death of the Kaiser would be the beginning of German troubles. Austria still joined with Germany since the treaty allowed it, but the conflicts got worse. Eventually, German Empire split between two heirs; the Prussian Empire (eastern Germany/Prussia along with northern Poland with Lithuania and later the rest of the Baltic states) and the Austrian Federation (The rest of Germany and Austria.) Austria is considered more the heir of Germany while Prussia has changed due to the Baltic influence (especially during the so-called Gothic Reniassance when Prussian embraced its Eastern Germanness). Heck, Baltic Prussian is considered a different language as of 10 years ago instead of just a dialect. They've definitely patched things up over the years so it's not too bad.
Hungary meanwhile is now one of the smaller kingdoms longing for past glory and a tendency to suck up to the USA (though this did mean they were the first East Europe statement to help with post-colonial Africa and in the USA, the Eastern-Europe immigrants and Afro-Americans have close relations). Bulgaria hasn't changed that much outside of being the babysitter of southern Europe.
The autotonomous state of Poland that the Prussian Empire kept would be merged with Czechoslovakia after the A/H fell and became the Wenden Kingdom, a collection of the West Slavic states. It stood on the sidelines for the most part, though Prussia gave them part of Silesia back in the 80s.
Besides the big powers, Africa also was a change. Darfur and the Dervish state became autonomous states rather than colonies while the Somalian colonies would end up in the Ottoman's influence, much to the annoyance of Ethiopia when they had to give up Ogaden (though the Eritrean territory dispute was solved when the Ottomans said it was theirs) so things worked out for them.
The lack of war in the US meant there wasn't an outlet for the growing tensions caused by the rich/poor divide, especially during the American Depression. This lead to the dominance of the Republican party (or the Neo-Whig Party as it was jokingly called) under Franklin Delano Roosevelt. Granted, the Pacific War helped out too in terms when FDR got involved after the attack on Pearl Harbor after years of tension due to Japan disrupting US-Chinese business relations and the resulting embargo.
Russia... well it's Russia. They left the war before the Bolshevik Revolution which was put down due to the White Coalition. They had a reactionary government for the first few years... before they were voted out due to gross incompetnence and being little different from the Tsar. The Mensheviks helped alot with modernizing Russia, even if most of Europe was wary of the socialists (though the Mensheviks fighting and leading the White Coalition did warm relations though.) Beyond that, they minded their own business outside of getting invovled with Mongolia's war of independence and later in the Pacific War when Japan thought they could take some land from them. Led to better American-Russian relations however. Heck, some have joked the Ainu protectorate state in South Sakhalin is their kid, given how Russian and American traditions have helped the Ainu modernize.
China eventually became a Great Power again years after the Pacific War and has strong relations with the US.