Another puzzler on the Fanucci front....

I know the book alludes to Marazano (Fanucci's boss/Don/head of family) being taken out in years to come, but that is never discussed in the film.

Part II has Fanucci, who was only a collector for that neighbourhood, being taken out of the equation. Why did Maranzano not simply put someone else in his place? Why was Vito allowed to suddenly rule the roost in the neighbourhood?

It strikes me as odd that a man as powerful as Maranzano would simply give up control of a money making Italian neighbourhood without so much as a whimper.