It was the spark that ignited the fire, but the kindling was already there. It probably still would have happened without his assassination, though possible a few years later.
There's also plenty of kindling in the world today. Plenty of current top players and upcoming top players butting heads(China and Turkey being the most news worthy to Americans), plenty of players that are sour about past/present conditions (Britain with Brexit, Germany/France over their influence in the EU), and players that are seeking allies to become an upcoming top player (India being the easiest to point out).
Plenty of friction indeed, but the big difference is that (almost) nobody wants to go to war. Just before WW1, everybody was itching for another war. China definitely does not want war with the US; they want to expand economically. Nobody in the EU wants war over anything. The US has always been the most eager to go to war, but even they seem to have learned that wars are expensive and have little benefit. Russia wants to control (pieces of) their neighbours, but again without an actual war the EU or NATO. Turkey is primarily interested in crushing anything that might start to look like a Kurdish state, but also doesn't want a war with a big player.
Wars today are mostly cold or proxy, and rarely direct.
