I read an all but lost expose about World War One, aka, "THE GREAT WAR" that exposed steel and wire manufacturers as the leading culprits whose goons caved in skulls at anti war rallies.
The end of opposition to the US entry into the war was not spontaneous or naturally occurring. It was the result of soldiers, sailors and trade union thugs who were used to suppress any gatherings with force. Imagine attending a rally or speech at a church and being set upon by club wielding "patriots"!
It was also combined with a propaganda campaign, and just as it was when Bush said that we're "either with (him and his Carlyle group buddies) or with the terrorists" there was only one side to the debate in 1915.
And, powerful forces (wink wink) guaranteed the US entry in exchange for The UK's support for The Balfour Declaration.