I think that the war brought about an attitude on a global scale that was very destructive. It encouraged various countries to think about getting their own way, regardless of the consequences, because they wanted to get revenge or to keep other countries down.
This attitude led to WWII as Germany sought revenge, as Japan sought to further its goals via violence, as France and Britain tried to keep Germany down, etc.
So I think that it weakened morality on a global level and led to WWII.
I would agree with the first post in that the United States came out of the war as a recognized world power and had the opportunity to become a world leader. I am not certain that we took full advantage of that opportunity.
The impact of World War I on America and global society was divergent. America felt a sense of unity and nationalism in its entrance into the war and felt a sense of power about being able to enter the war and swing momentum towards its direction. At the same time, I think that being able to see its nation stand with success and a sense of victory in its possession while the rest of Europe was fragmented and completely destroyed as a result of the magnitude of the conflict helped to differentiate America from the rest of world. America emerges as an unprecedented world power after World War I, but does so in a world of uncertainty. The distrust of foreigners, as evidenced in the trial of Sacco and Vanzetti, the passage of the Espionage Act of 1917, as well as the Sedition Act helps to bring about much in way of paranoia about the rest of the world. While America was seen as a world power after the First World War, Americans, themselves, preferred isolationism from the global society. This helped to create a disconnect in the years that followed, with America possessing the capacity to be a world power, but lacking the consensus or will to do much about it.