Has World War I or 2 had a larger impact on the world today?
I would like to point out that the Versailles Treaty ending WWI contributed to the start of WWII along with other factors.
The consensus of military historians and sociologists these days is the World War 1 has had the most far-reaching consequences of any conflict in the last 200 years. While of a considerably smaller size than WW2, a huge number of later conflicts and social movements are directly traceable to the manner in which WW1 was fought, and the way that it was concluded. Here are some outstanding examples:
- Rise of Nazi-ism: the peace treaty ending WW1 (Treaty of Versailles) imposed harsh (many say unreasonable) conditions on Germany and Austro-Hungarian Empire. Nazi-ism's success in gaining adherents was primarily caused by the weak Weimar Republic government of the 1920s Germany, which was weak almost exclusively because of the conditions imposed by the Treaty of Versailles.
- As a corollary to #1, the peace treaty after WW1 is usually held directly responsible for the start of WW2, both in Europe and in Asia.
- Change of warfare from contests fought between rival armies, to one where the entire national economies were involved. This is often called the change to "total war". Total war is hugely destructive, since in a total war, everything is a valid military target - civilian factories, for instance. Death tolls and destruction levels go up radically in a total war conflict.
- Conflicts in the Balkans in the 1990s is due to the badly-drawn and created countries in that region after WW1.
- Similarly, much of the continual African civil wars and fighting is due to the collapse of the German Empire, and the severe weakening of the French and British Empire that WW1 caused.
- It is extraordinarily unlikely that Russia would have become a Communist country if not for WW1. In fact, it is unlikely that Communism would ever have been considered a valid form of actual government in any country if WW1 had not allowed for a communist takeover of the Russian Civil War in 1917.
- No Communism, no Cold War. No McCarthyism. No massive defense buildup of the USA.
- The military dominance of the United States after 1940 would almost certainly never occurred, and it is likely that the USA would not be a strong international influence - we would most likely have retained the very strong isolationist streak prevalent in the US pre-1914.
- The breakup of the British Empire is primarily due to WW1, not WW2. Britain came out of WW1 essentially bankrupt, and consequently was slowly losing its grasp on the Empire, as they could no longer afford to protect and govern it as well as needed.
- If WW1 has not ended as it did, WW2 would most likely not have happened, and the whole host of horrors from that conflict would never occurred. No Atomic Bomb. No Holocaust. No rockets (and, probably no Space Race or Man on the Moon). No nylon.
- The mass slaughter of the Western Front radically changed Western thought. It had a drastic impact on Literature and Philosophy, and a corresponding influence on popular culture. The change is much more radical than any similar one after WW2.
- WW1 changed the power structure of the world from a Europe-centric view to a Global view, with the rise of several non-European Great Powers.
There are many others, but the historical consensus is the while smaller, WW1 is much more influential than WW2.