By JONATHAN MATTISESean “Diddy” Combs is set to be sentenced Friday for violating the federal Mann Act, an anti-prostitution law with a century-old history. The Mann Act makes it illegal to transport someone across state lines for the purpose of prostitution or other illegal sex acts. The law was amended in the 1980s and today a lot of Mann Act prosecutions involve people accused of taking children across state lines for sexual purposes. Why it’s called the Mann ActIn 1910, Congress passed the bill, which was named after Republican U.S. Rep. James Robert Mann of Illinois. Combs was acquitted of sex trafficking and racketeering charges but convicted of transporting people to engage in prostitution.