The point, to me at least, is very blurred and varies from the sources you speak to or read about. It was war on war, country on country, a mass domino effect leading to millions of mass death and injury, ripping apart families, and traumatizing the masses. What was gained? some treaties of course, and military advances in technology and strategy but at the end of the day, the only real things gained were a couple of tanks and guns, only ever to be used for more death and killing in the future. Lots of people may talk about how we made lots of good advances in technology and innovation but what was accomplished from those? to me at least it all just feels very artificial, no one really gains anything and everyone loses something and or someone. I think it matters since it serves as a type of warning, one telling people that if they are not careful then 16 more million people could be killed. While many were loft, people gained a new sense of connection with other countries, playing soccer on Christmas, deciding to hold off the war for the sake of a party and I'd like to say it stuck around for a while but then ofc there was a second world war waiting right around the corner.
I think we learned that the countless lives lost, economic downfall, and huge cultural shifts were large all the effects of men flexing their guns at each other and it wasn't worth it at all. It is very hard to say what we learned though since the nazis would soon take over Germany about a decade later, cruelly slaughtering in the millions for their "cause" and the planet was yet again thrown into a war. It leaves me very conflicted because I would like to say we made advances in a sense of community among the countries, swooping in the save the Jewish victims of the Holocaust, which I guess one could argue, could be a result of how WWI affected everyone but at the same time we may have done that anyway. At the end of the day, I would hope we should learn to try and understand each other, look at the bigger picture, not be merciless killers, and that each and every human life matters.
In some aspects yes I would say that there are different worlds before and afterward like how before, younger kids and teens viewed war as "a big game" and would happily join up, lying about their ages, running from home, and doing whatever they could to get themselves in the army but, once this war ended I think people had a more realistic view of war, the water lugged trenches, corpses everywhere you turn, lice thriving off your clothes and skin and mud to slick and deep you would drown. It was viewed less as an act of blind patriotism to join the war brigades but as a sacrifice for your country instead, not really a lighthearted decision to be made, and people didn't have the same, happy and charismatic ideas about the army as they might have had beforehand. Risks with forboding wars these days are much more to worry about as well, with nuke threats at every corner and spy balloons in every cloud, people are much more paranoid and don't know what to do with themselves. In general, I would say that the population is much more sensitive around the subject of a worldwide war and they (I hope) wouldn't make the same decisions they made before.
We need to understand the history and what leads up to events so we can try and prevent it in the future. I can guarantee that we don't want history to repeat itself because if it did we might end up without a planet to call home. We need to recognize the effects that wars have on everyone and give homage to those who died for peace by keeping it, what is war if not a mass destroyer of hope?