The problem it caused was that many country leaders thought that since the royal Duke was trying to bind the Austria and Russia together with his reign, and was killed by a Serbian, the nations got worried. Austria lost one of its would be ally. In short, every country wanted feel protected, since war was bond to breakout. That is why the Allies and Central Powers fought against one another. There was a country's king, I think, sent a letter of his declaring of war to his cousin (a Central power leader), saying "We played war as children...why do you wish to fight me...Fine then, let's play war..."