Oscar's right, the mobs power in the Teamsters were mostly through Mid-West families, like Chicago and Detroit, being the big one and most obvious and spoken about. Size wasn't the ultimate factor, it was mostly about the connections made, Kansas City is in this group too, that's how they got connect to a president, through corrupt union men who'd made those connections, rubbing elbows with local politicians, who were then backed with union/mob money into gaining more prominent, federal positions. Gus Russo's The Outfit book goes deep into the union connections Chicago had and how they got them, as well as a whole section dedicated to Kansas City & Truman.