I too have heard that all Sforza's are related and that they were the family that ruled Italian military for centuries.
I only have one connection to the Sforza line: a marriage between Maria Sforza (1868-1960) to Antonio Grande (1864-1943). I connect them to Bari, Italy because I know that they originated in Italy and their grandchildren are listed as being born in Bari.
ANY information you could give me would be helpful. I don't know Maria's parents names or if she had siblings!
Thanks!