While the root causes of WWI were minor, compared to those of WWII, we're observing "The Great War" through 21st century eyes. The alliances formed in Europe were always problematic, because those alliances weren't well thought out. They seldom looked past their allies' far borders, and created more problems than they solved.
By the time WWI ended, not a lot understood why or how. The Germans were handed almost all the blame for the war, yet they were not a primary belligerent. That ignominity goes to Austria-Hungary and Serbia. And the end game to the war sowed the seeds of the next.
The victors imposed huge reparations on Germany, because thats who the French and British wanted to pay the tab.
The war ended up creating whole countries with little, or no, geographic or political sense. Iraq and Yugolavia come to mind.
World War I was an opportunity to settle old scores; the French got back at Germany. Britain pushed the Ottoman empire back to Turkey, and claimed large chunks of the Middle East to fuel its industrial growth. So, there were very few clean hands in the mess.
The U.S. was perhaps biggest the winner. Woodrow Wilson failed in his nation building policies, and the U.S. managed to leap to the head of the economic world, where we reside today, abeit tenuously.