Which 2 baseball teams were in the first modern world series?

The inaugural World Series of 1903 was a resounding success and represented the first step in healing the bruised egos of both the veteran National and fledgling American Leagues. Pittsburgh and Boston went head-to-head for eight games (The Boston Americans defeated the Pittsburgh Pirates 5 games to 3) proving that great baseball between the two leagues was possible and that a merger would benefit the growth of the sport.

After two years of battling each other over players, the established National League and upstart American League signed a peace agreement before the '03 season. It wasn't until August that their owners agreed on a so-called "World's Championship Series," best-of-nine format.

The Boston Americans were commonly referred to as the Boston Pilgrims which was their nickname. This was because of a poem & song by Rory O' More called "The Pilgrims at Home". This poem/song can be found here.