Just after Michael killed Solozzo and McCluskey, the police cracked down on all Mob activities. "An emissary from the Five Families" asked if the Corleones would give up the murderer. The emissary was told it was none of their business. Then murder and mayhem began--"the Five Families War of 1946."

This was a long war, and ended only after Sonny was killed and Vito needed to bring Michael back from Sicily. I can't believe it was only about the Corleones giving up the murderer, since the novel (and the movie) tell us that the police had begun to loosen up, for good reason (pay off mortgages, put kids through college). What was the war really about?

I think there's several things. I think the widest war was set off by the killing of McCluskey. This was Vito's legacy - he had set up ten years before a system of conduct, and the Corleones breached that. The other families, who had previously been recruited into the system, were now required to set upon the Corleones until the Corleones fell back into line.

Second is the drugs business. The families were probably seeing freelancers make a lot of money, and realized both the threat and opportunity in that. To gain control over that business, the families needed to deploy their advantages over outsiders, and the Corleones controlled several of those functions. Again, the Corleones had to be brought into line.

Finally, I think there's also an opportunistic grab for power by Barzini. He'd be pushing in any direction, no matter the issue, with the goal of chipping away at the Corleones.

Pete, I agree with your second and third points:
I'm guessing that, after Vito turned Solozzo down but Sonny showed interest, Sol had to get permission from all the Dons to attempt to whack Vito. He probably had to promise them a piece of the drugs action with the assurance that Sonny wouldn't go to war because Tom would convince him to make the deal. Even after Sol was whacked, the Dons probably saw the potential of drugs and either began or planned to pursue drug trafficking. They needed Vito's judges and politicians as much as Sol did.

And, yes, Mob wars are always about money and power. Barzini saw not only drug money, but the opportunity to become Numero Uno.

The book is ambiguous as to how the war was fought. Sonny's attempt to take out the heads of the other families implies that they were all combatants, but the peace conference chapter just says Barzini supported Tattaglia "with money and influence." There's no reason to think of Cuneo and Stracchi as combatants, except that the war was called "The Five Families War." On the other hand, it's hard to imagine Phillip Tattaglia holding the line alone against the Corleones for any length of time.

Pete, the novel states that it became apparent that the Corleones could match the other families gun for gun, but that they had overmatched themselves. Further, it states that the only way the families could stave off defeat was to murder Sonny. I assume that means all of the other families.

I just downloaded to my Kindle.

Amazon having a one-day sale today $1.99

I almost paid $12.99 last week, good thing I was too lizzie to read. since its next on my list.

I hope I make it through the chapter about the broad.

Power and money of course. The main issue was Vito's connections to politicians and judges, that the other families felt they too should have a share of them. The books mentions the commission, and why the families heads did not meet with Vito about Solozzo drug deal and Sol meeting with Vito shows a sign of disrespect, especially at his daughters wedding. Instead of having a meeting with Vito, the other families backed up Tattaglia, which doesn't make much sense until you put Barzini in the equation for the movie. The book is different, and Cuneo and Stracchi did not go after the Corleones until they refused to give up the murderer after the police started to crackdown on the families revenue. The book also tells that the other families were interested in the drug business, but wanted to make sure that Vito would back them up with his political connections. How M.P. set the story up, we get almost right down to what the story is going to be about on the surface, and thus why MP took short cuts in writing the book.