The Lost Generation included not only Fitzgerald and Hemingway but Gertrude Stein, Ezra Pound, John Dos Passos, and T. S. Eliot. The Lost Generation was influenced by a lot of things, but here are a few:
1. Modernism. All of these writers are widely known as "modernists," meaning they were influenced by what they saw as a rapidly industrializing society that was quickly moving out of an agricultural life and into an urban, city-based life. Many modernist writers felt that this transition caused people to be alienated from one another even as they were constantly surrounded by people.
2. World War I. At the time, nobody in living memory had ever seen a war as brutal and mechanized as World War I, which many of these writers participated in. This war introduced these writers to the brutality of chemical weapons, trench warfare, and shockingly effective new weapons like the gatling gun. The result was the idea that humans were a victim of their own ingenuity, as they had created forms of technology that threatened to destroy their own species.
3. Life abroad. The Lost Generation is called "lost" because many of them left their homes to live in other places. Stein, Hemingway, and Pound were all Americans who moved to Paris and Italy. Eliot was British, but lived in Paris as well. James Joyce was Irish, and wrote almost exclusively about Ireland, but did so from his homes in Paris and Italy.
4. Each other. One interesting thing about the Lost Generation is that many of these writers were very close friends with one another and helped each other write and edit their books. Pound helped Eliot write the famous poem "The Waste Land," Stein helped Joyce publish the novel "Ulysses," and so on. Hemingway even wrote an entire novel called "A Moveable Feast" about all his writer-friends and their lives in Paris. That novel is where we get the term "The Lost Generation."
