World War I affected the world in some tremendous and long-lasting ways. Here are a few:
- It led to WWII. World War I, and the Treaty of Versailles that was reached after the war, set the stage for WWII to occur. These things left countries like Germany and Japan unhappy with their place in the international system and (in the case of Germany) thirsty for revenge.
- It helped lead to nationalist rebellions among colonized peoples. This happened both because colonized people came to see that the Europeans' civilization was not so wonderful as advertised and because of President Wilson's advocacy of self-determination for all ethnic groups (at least in Europe). These things helped to lead colonized peoples in places like Vietnam to eventually rebel against the colonizers.
- It helped to reduce people's faith in the inevitability of progress. Up until the war, most Westerners had believed that society was moving inexorably towards perfection. They believed that society would always progress, getting better and better. When this horrific war happened, that faith was shattered.
- It helped bring about the idea of international institutions like the UN. In the wake of WWI, the League of Nations was set up. It failed, but it laid the basis for the creation of the United Nations after WWII.