Jesus, I come to this sub trying to procrastinate on my paper about Christopher Clark's the Sleepwalkers and all of a sudden this pops up? Oh dear. I'll try not to spend too long here. I also highly, highly, highly recommend reading that book in order to understand the background of World War I.

Serbia had been fighting wars against the Ottoman Empire and other Balkan states for quite some time in the pursuit of self-determination. While Serbia had managed to create a national state for itself, many Serbs (approximately 50% of the total Serbian population) lived outside of its borders. Drawing inspiration from a medieval Serbian empire, Serbian nationalism was all about expanding big time to create a Greater Serbia and encompass all Serb nationals. This led to the aforementioned wars against the minor/failing states of Bulgaria, Greece, the Ottoman Empire, but what about the Habsburg Monarchy?

The Habsburg Monarchy was, despite the modern conception, a highly successful multinational state able to placate various nationalisms better than most contemporary states. It also included a ton of Serbs. Franz Ferdinand was close to succeeding the throne (Franz Joseph was 83 in 1914) and was super liberal about national self-determination. There was a serious fear by Serbian ultra-nationalists (of whom the Black Hand are the most pertinent to this topic) that a Franz Ferdinand led Habsburg Monarchy would allow Serbian nationalism to fade out since all the Serbs in the HM would have full rights and access to greater economic opportunities than they would in Serbia.

Then, he's also the figurehead of the Habsburg Monarchy which had been agitating against Serbian foreign policy. Serbia had been seriously expansionist in the first decade of the 20th century, increasing its total territory and population by about 50%. Habsburgia was none too pleased about this and was threatening intervention, or at least militarily enforced detente in the region.

Finally, Franz Ferdinand decided to visit Sarajevo on the anniversary of the battle in which the Serbian Empire had been destroyed in the 1300s by the Ottomans at the Battle of Kosovo. Not great timing. This was the first time Serbia had owned Kosovo in centuries, by the way, so hype was high.

Alright, I really gotta finish this paper. As for your second question-what effect it's had? Dude, like all the effects. If The Sleepwalkers demonstrates anything, it's that WWI was totally dependent on contingent factors, especially this one. Without WWI the 20th century is unrecognizable.

To all readers: go out and read The Sleepwalkers. I had to cram it into a couple days-not recommended, but it was still an amazing expose, both at why WWI happened, and also how truly exceptional historical inquiry can be. The book is a masterpiece.