How on earth does this relate to WW1 at all? WW1 started because a Bosnian-Serb assassinated an Austrian duke, and when asked to investigate Serbia told Austria to fuck off. Serbia was a completely separate country to Austria, and was purposefully trying to stir up shit in Bosnia and Herzegovina.
This was a U.S. citizen trying to assassinate a former U.S. president. Nobody else in the world is going to give a shit. We actually do this with startling frequency compared to most other countries.