In the first chapter of the novel, Nick explains that after he graduated from college in 1915, he fought in the Great War (World War I). His explanation of what happened when he came home, however, is somewhat curious. He says,
I enjoyed the counter-raid so thoroughly that I came back restless. Instead of being the warm center of the world, the Middle West now seemed like the ragged edge of the universe—so I decided to go East and learn the bond business.
Seven years after he graduated from college and three years after the end of the war, Nick moved from the Midwest, his home, to New York City. However, the fact that he says that he "thoroughly enjoyed" any part of fighting in the largest scale war known to humankind at that stage in history is odd. So many people, soldiers especially, had their worldview completely reshaped as a result of this war. There was so much bloodshed, the result of new and more powerful weapons, that people became terribly disillusioned as a result.
So when Nick says that he thoroughly enjoyed the counter-raid, he is likely speaking euphemistically because he learned that the old adage is true: you can never go home again. He tried to return to the Midwest, his home, and he found that it no longer suited him. It didn't feel like a warm and comfortable home anymore; it seemed far away from everything, somehow insubstantial.So, where can one go that would feel vital and busy and important? New York City, he decides—specifically Wall Street, as Nick says,
Everybody I knew was in the bond business, so I supposed it could support one more single man.