When the Assassination attempts failed the arch-duke of Austria Franz Ferdinand went to visit some injured officers (that had been injured by the failed assassins) in his opened top car and got killed by one of the failed assassins. If he had gone into hiding instead of going back out in his car the world would not have had the war and so WWII would have been prevented because the treaty of Versailles never happened (the treaty caused the war to happen). Millions of lives would have been saved and also people hopelessly mutated by mustard, Chlorine and many other types of gasses would have been able to live a free life that has not been affected so greatly.
Even in 1914, Belgium feel threatened by UK due to Colonial disputes and was getting closer to Germany.
Simultaneously Germany & UK were finishing a Naval Agreement which would have prevented any conflict between the two.
Secondly if the Austrian Emperor had died in 1914 instead of 1916, Balkans would have been irecognizable.
No one cared about some duke getting killed, Sure he was important but that was not why they went to war. That was just the excuse nations were looking for to go to war.
The Germans had it in for the British and other nations had their own reasons for going to war.
Even if the Duke avoided the assassination, The nations would still find another reason to fight. The Germans were ambitious and a lot of Europeans nations hated each other believing they were the best nation.
And look at today. We might go to war on the whims of a few people. Some people are itching for fight and want to fight with Russia or China. They are just waiting for a reason to.
Yeah so world war 1 had to happen exactly as it happened because everything is caused by something before it so nothing else could of ever happened. Even with a time machine If it’s possible there would be the time travelers trying to start ww1 and the time travelers trying to prevent it fighting in the past changing the present so that they themselves never existed to go back in time to do what they did with time travel.
Everyone wanted something in WWl. Killing the Arch Duke only set things in motion and was an excuse for war. Even if they didn't kill the Arch Duke they would have found another excuse to go to war. WWll could have been prevented but WWl was inevitably going to happen.