The Origins of Baseball... date back to the 18th century and was only played by amateurs until the 1860s when professional baseball clubs began to be formed. The National Association of Professional Baseball Players operated from 1871 to 1875 and is sometimes considered to have been the first major league. During the end of the 1800s there were a number of leagues that formed (and most disolved relatively quickly) such as the Union Association, Players League, American Association, Western League, National League and dozens of other, smaller clubs. It wasn't until the first years of the 20th century when the American League and the National League cemented themselves as the dominant leagues in the United States and the first World Series were played.