Much has been written about the causes of World War one, and it must be noted that as a result of the First Balkan War, the Balkan League (Serbia, Montenegro, Bulgaria and Greece) drove out the Ottoman Empire; and the Second Balkan War which saw Bulgaria attack its former allies, probably laid down more root causes for yet another conflict in Eastern Europe than anything else.
The reason why Franz Ferdinand was in Sarajevo in the first place, was as part of a state tour which included opening a new museum and observing military maneuvers in his capacity as Inspector General of the Armed Forces of Austria-Hungary. Basically, the job was seen as being beneath that of the Archduke's wife, Sophie, the daughter of Emperor Franz Joseph, for her to officially represent the imperial family.
Perhaps justifiably, the people of Serbia, didn't particularly like the imposition of yet another foreign power exerting control over what they thought should their lands (or at least their slavic cousins' lands) and so when word got out that Archduke Franz Ferdinand was going on his tour which was kind of semi-deliberately designed to give the locals the angries, a Slavic nationalist by the name of Gavrilo Princip, was one of a group of about seven people called the Black Hand who intended to change Franz Ferdinand from being still alive to not still alive. All of them were armed beyond anything remotely reasonable; some had grenades and high-powered rifles. If Princip wasn't the one who was going to do Franz Ferdinand in, then at some point, one of the rest of them would have.
Princip would later state at his trial in which he would be sent to prison for 20 years (being seven days too young to be given the death penalty) that:
"I am a Yugoslav nationalist, aiming for the unification of all Yugoslavs, and I do not care what form of state, but it must be freed from Austria."
Gavrilo Princip would later die in prison from tuberculosis; most likely as a result of the conditions in prison.
From what I understand from here on, the chain of events was that war happened between Serbia and Austria-Hungary, Serbia called for the help of Russia, Austria-Hungary called for the help of Germany in preparation to stop Russia who were sort of allied with Serbia, Germany asked France if it would remain neutral if it declared war against Russia and France said "non", Germany declared war on Russia and the declared and alliance with the Ottomans and then after France stated that it would not remain neutral, declared war on France.
Get it? Got it? Good.
Germany tried to exact a plan called the Schlieffen Plan which involved marching through the Low Countries of Belgium, the Netherlands and Luxembourg before marching into Paris but the English didn't stand for that and came to the ally of France and the Low Countries and the whole affair basically came to a grinding halt, that spat out millions of dead bodies, killed a great deal of the working classes of most of Europe and would sow the seeds for World War 2.
During all of this, chemists on both sides invented ever more evil ways of killing people, the influenza virus, poor sanitation and poor medical facilities to deal with the wounded ended up killing more people than machine guns ever could and a lot of moustachioed generals got a heap of shiny medals to pin on themselves.
If all of this sounds like an over-simplification of a conflict which raged on for four years, then it probably is; but be mindful of the fact that virtually none of it really makes any sense at all.
I personally think that choosing to fight for one's country is among the most noble of professions and it incenses me when commanders and particularly politicians invoke nationalism, patriotism and religion in the name of sending other people's noble children to fight in foreign lands. I wish that I could find the quote, but I read somewhere that mens' lives are the coin of the realm of the battlefield and that that is how you buy territory and tactical advantage.
Well I'm sorry but I'm pretty sure that the parents of even the most heroic sons, would still prefer to have their little Billy returned safely home to them, than a small teak box and a Victoria Cross with the words Sgt. William Jones in place of him, if he lies dead somewhere in a field which in five years time will become the home of sheep and cows.
One of the biggest lessons of the First World War that should be really really obvious and writ large in crimson letters of the blood of almost 40 million people is that if only people had thought just a little bit harder and longer and not engaged in so-called "military diplomacy" then none of it need ever have happened.
If Franky Ferdy had got out of bed one day in June of 1914 and thought "You know what, I don't really need to annoy all these people. I think I might go home to Vienna for some tea, biscuits and Sachertorte", then June 28, 1914 might just have been another sunny summer's day in Sarajevo.