This is a difficult question to answer since it is so vague. There are many things that could be said as one reflects on this war. My own view of this war is that it was, perhaps more than any other war in recent history, a tragic waste.
WWI was not really about a big idea. This was not a war against fascist aggression like WWII was. It was not a struggle for democracy and against communism. Instead, it was a war that was really just about power. Germany wanted more power. As it tried to get more power, it frightened countries like Britain and France. The countries’ desire to get more power or to keep the power they had led to the war. This is not a really good reason to have a war.
WWI was also a war that wasted human beings. This war is infamous for the trench warfare on the Western Front. This was a war in which generals ordered men to engage in what were essentially suicidal attacks. It was a war in which constant shelling broke men’s minds. It was a war in which armies used chemical weapons against one another. All wars are brutal and wasteful, but this one was worse than usual.
Thus, I see WWI as a tragic waste because it threw men’s lives away for very little reason.