What is one reason why marx would disagree with this statement?

Marx disagreed with that statement because it lacked the element of revolutions.  For Marx, in order for effective change to come about you have to get rid of the old order through revolutions so that it is totally taken out and to allow a new system to take root and flourish.

the united states broke it's neutrality was the constant german sinking of trading vessels resulting in the loss of lives, one example would be the lusitania.