how about the soldiers in the trenches having a ceasfire for christmas and exchanging presents with their opponents? bit positivity instead of doom and gloom if you want details or some analysis im gonna shut up now edit: for better answers i think you need to narrow down the range of your question, like from how far back, from which point of view do you want to look, and into how much details do you want to go
I think you're the one going off-topic. Ice backed a comment saying Jews caused WWI, implicitly stating that Hitler learned his anti-semitism from Russia in WWI. It's nonsensical. Also, WWI directly led to WWII. Trying to separate the two topics seems a bit narrow
The actual assassination was a horrible, bungled affair. The real reason WWI started was because the drivers were idiots, and couldn’t read maps. https://en.wikipedia.org/wiki/Assassination_of_Archduke_Franz_Ferdinand
The reasons for the Great War were many, you couldn't really point out a singular defining reason for everything that occurred. Europe was changing at the time and industrialization had just occurred, there were a lot of new weapons in circulation and everyone was a bit too eager to actually use them. Germany had just become a thing a few decades earlier after Prussia managed to solidify itself as the go-to power for the Germanic tribes as opposed to Austria. Prussia by itself was already a major European power so as soon as Germany came onto the European stage it was quite the force to be reckoned with and it wanted to grow its power and influence to match the likes of the other European powers such as France and England that had been around for centuries and had colonies that spanned the globe. The specifics are quite well-explained here: I'd only add on that in addition to the high tensions between the various Empires of the time, the last Major wars to have happened were the Napoleonic Wars. To the Europeans at the time, a war was still something of Glory and Valor. The assassination of the Austrian Arch Duke by 'possibly' Serbia was indeed the trigger that kicked the war off, but Austria only declared war because they had the backing of Germany. Serbia's ally was Russia, and Russia's ally was France. The War started out with Germany and Austria facing off against those three powers. Germany's plan, the Schlieffen Plan, was to quickly take France out of the War then turn around a beat Russia to avoid a war on two fronts. This was supposed to be a good plan because Russia, though massive, should've taken a while to mobilize and if they could possibly defeat France before the Russians could mobilize then they would be able to pull all their forces from the Western front and focus on the East. It was mentioned before that Britain and France were allies, but Britain wasn't all that keen on helping France against the German invasion. Britain was only provoked into the war when Germany, trying to get around the heavily fortified French defensive lines, invaded Belgium. The invasion of neutral Belgium is what finally pushed the British into the war. The Great War, or the War to End War as it was also known, ended up severely scarring all the nations involved and ended with the dissolution of the Austro-Hungarian, Russian, German, and Ottoman Empires. However, the results of the war and the heavy penalties imposed by the Treaty of Versailles simply set the stage for World War II. You can see a video on World War I here:
Should be mentioned that the germans didn't just promise the austrians unconditional support, they urged Austria to attack quickly and defeat Serbia before Russia could mobilize and while sympathy was still high for Austria following Ferdinands assassination. Austria instead spent weeks trying the diplomatic route by giving Serbia ultimatums, which ultimately failed and had given Russia more time to prepare before the war broke out. If a quick attack would have made a difference in the long run is up for debate, but it is just interesting how much of a mess the whole month leading up to the war was.
Should look into why the Ottomans joined Germany, some factors include the British stealing two battleships they were making for the Ottomans, and the British ambassador and staff couldn't speak or write the local language.
Nationalism gained popularity in that ages, and the Balkans are just timebomb keg filled with fuel readied to explode when the spark lit. You see this two combination? Add chain aliance in the equation, you get complex chain reaction enough to decimated half the world.