Baseball is America's most popular sport. In a baseball game there are two teams of nine players. Players must hit a ball with a bat and then run around four bases. A player who goes around all the bases scores a run for his team. The team that finishes with more runs wins the game. Where did baseball come from? No one knows for sure. Many people believe that the idea came from a game played by children in England. Other people believe that a man named Abner Doubleday invented the game in Cooperstown, New York, in 1839. But the first real rules of baseball were written in 1845 by Alexander Cartwright. Two teams from New York played a game following Cartwright's rules. The rules worked well. Soon there were many teams. These early teams were not professional. They played only for fun, not money. But baseball was very popular from the start. Businessmen saw that they could make money with professional baseball teams. The first professional team was started in 1869. This team was the Red Stockings of Cincinnati. Within a few years there were professional teams in other cities. In 1876 these teams came together in a league, or group, called the National League. The teams in the National League played one another. In 1901 a new league, called the American League, was formed. To create some excitement, in 1903 the two leagues decided to have their first-place teams play each other. This event was called the World Series. Each year since then the National League winner and the American League winner play in the World Series. And, each year, millions of people look forward to this exciting sports event.