The song that was born from a broken guitar string! On this day back in 1970 (5/9) the Guess Who started a three-week run at No.1 on the US singles chart with ‘American Woman.’  The song was the group’s sixth Top 30 hit but their only chart topper.  According to rock and roll legend, the song was born by accident when guitarist Randy Bachman was playing a heavy riff on…