“....
Serbia’s response effectively accepted all terms of the ultimatum but one: it would not accept Austria-Hungary’s participation in any internal inquiry, stating that this would be a violation of the Constitution and of the law of criminal procedure. This response did much to appeal Pasic and his country to international observers of the conflict; to Vienna, however, it made little difference. ....”
https://www.history.com/this-day-in-history/austria-hungary-issues-ultimatum-to-serbia
I don’t know what was dumber, how WWI started, or the fact that the US decided to get involved in that stupidity.