If you're going to correct people do it right: It was Austria-Hungary and not Bulgaria.
Blimey, I wanted to have a long winded rant about that. I will go on anyway.
The event which many people consider as a starting point for the Great War was more like a catharsis of the 1867-1914 era. That time, the larger political entities could be divided into two groups, the ones who started colonisation early and had vast amount of colonies and lands (England, France, Russia) and the countries which were late to the whole colonisation game (German Empire, Austro-Hungarian Monarchy etc.).
Also, during that time the Ottoman Empire was dying and losing many territories in the Balkans which meant that new countries were born, but it came at the price of instability which is why the region was considered as a "barrel of gunpowder". There were two Balkanic wars, the first one broke out in 1912 and ended in 1913 (Christian nations against the Ottomans) just to have the second one break out two months after the first one since Bulgaria was bitter and dissatisfied with its share in the first one; during the second one territories were lost. This made Bulgaria side with the Central Powers. (Not to mention that many countries wanted to colonise the Balkan Peninsula).
Now to be more simple from this point on, the usual political games and the tension between the countries that colonized early and the newcomers that demaded "their share of the cake" resulted in that basically every country was just waiting for an opportunity to have that war started.
Also, remember kids, the Second World War was a
direct consequence of the unjust and harsh treaties that marked the end of The Great War.
