If you think about it, do you think Solozzo is the first person to come to him with an offer like this? Hell no, this is New York city, drug trafficking didnt start in the 1930s or the 1830s. It started with the beginning of human travel and settlement. Along with uncut diamonds, alcohol, humans, and any other form of matter that a person was willing to pay/trade for.

Barzini gave Solozzo direction, told him the best way to go about getting what he needed to become New York's drug kingpin.