Generally, the World War I was taken with a sort of enthusiastic patriotism across countries of Europe.
That wasn't the case, though, between the peace groups that were starting to get loud. Those groups were actively condemning the war. It came to the point where some people were getting arrested for denying being a part of it.
Those groups were also very much against one more country joining the war. In this case, the USA. Also, in the US, labor unions, socialists, members of the Old Right, and pacifist groups in the United States publicly opposed participation.