The 5 Main Causes for WWI
Archdukes, Cynicism, and World War I: Crash Course World History #36
HOW World War I Started: Crash Course World History 209
Who Started World War I: Crash Course World History 210
Countries went in to a arm race preparing their army with weapons, training, and improving natives.
Alliances in WWI would put middle school drama to shame! Countries were getting tangled up trying to attack countries that attacked there alliance and then they would be attacked. Basically it would be a big mess.
Each country wanted to be the best of the best and assert power over everyone else thus causing attacks to prove that one country is better.
Larger countries were attempting to take over smaller countries. This would have been fine-ish if to larger countries did not fight of smaller countries.
A (Archduke Franz Ferdinand)
The assassination of Archduke Franz Ferdinand was the event to trigger WWI.