The Mets came into existance because of a nervous National League office. A renegade new Major League called the Continental League, was planning on becoming a third member of MLB, joining the American and National League systems. The "Continental League" was born in the office of William A. Shea.. a NYC attorney who decided that Major League Baseball wasn't doing anything to expand into territories that deserved Major League Baseball... and that included a second team in New York City to replace the Giants (who had left in 1958).