The first professional team was formed in 1869 (the Cincinnati Red Stockings), and it gained in popularity to become United States' “national pastime” in the late 1800s. The two major leagues were formed in 1876 (National League) and 1903 (American League) and the first modern World Series, pitting the two champions of the leagues against each other at the end of the season.
Because of the equipment, baseball in the 19th century was very different than today. Balls were "dead" and didn't travel as far, and players were looser with the rules involving spitballs and other tactics that are no longer legal.
