Which I will not be using for my fic. This is an actual, in canon thought.
Marcone is undercover for the US government. He's military and was sent in to help take down the Vargassi's. He went under, and he went all the way under. Something made him realize that his side taking down the Vargassi's wasn't going to be enough. Amanda Beckitt's shooting most likely being the final straw. And he just went ahead and took the hell over.
It would explain why his reach is national. It would explain why the FBI has had multiple investigations into him killed from higher up.
Sure, him being a bad ass criminal would also explain it, but it's like he has too much power in the normal world for a mob boss, no matter how good at his job he is.