I always thought it was just a film and not too get bogged down in the detail, but one thing that bothered me is the ending.

Michael has the heads of the 5 families killed and thereby "settles all family business"

Why should those hit gangs be subservient after that ? Were the Coleones (excuse spelling) subservient after Sonnys death (The affected leader) ? No way. Is not one of those gangs going to attempt some kind of revenge ? Of course they are, what kind of gangsters are they going to be otherwise.

I like the ending of the UK film The Long Good Friday when the gang leader (PLayed by Bob Hoskins) has the main players of the other side(the IRA) killed at a meeting at a racetrack. Then he thinks hes settled it, problem solved. Of course, at the end of the film when hes relaxed after his victory, he gets in a taxi. But the taxi speeds away, the drivers mate turns round and points a gub at him. Its the IRA, and hes had it. (The film ends there)

You're not wrong, Colin. In the film, Michael consolidated his power in New York by whacking the heads of four rival Mafia families, plus Moe
Green, plus Carlo. But in the novel, Michael only whacked Philip Tattaglia and Barzini, plus Carlo, on the Day He Settled All Family Business. He evidently reached an accommodation with the two surviving NY Mafia Dons (he'd dispatched Moe Green previously).
Why did the film deviate from the novel in this regard? Mainly to make for a far more dramatic conclusion through a surfeit of violence. Even so, we subsequently saw that Michael had no real peace. In a deleted scene, we hear from Neri that Fabrizio emigrated from Sicily to America "in 1956, sponsored by the Barzini Family." So even though Barzini was murdered in '55, his family apparently was intact and still making mischief against Michael. And, as we saw in GFII, the "olive oil business" that Michael had handed to Clemenza after the Great Massacre was now falling apart under Pentangeli.

The fact is, the (Italian-)American Mafia is not all about revenge, in contrast to the Sicilians where revenge and "vendetta" is a common theme. Business suffers if wars are going to happen. Throughout the history of the Mafia in America, countless Bossess have been executed with little or no retaliation.

Luciano having Maranzano killed.
Gotti having Castellano killed and this one is a good example because a relative of Castellanos (who wasn't in on the hit) made no move against Gotti or his crew.

My guess is, if the Corleone execution of the 5 Families was real. Michael would have allied with the Capos of the Families, promising them power of their Family and then no one could oppose them.

In the Novel, not only did he kill Tattaglia and Barzini but also there most operatiting officials.

I think the greater implication was to send a message : The Corleones were still capable of defending their territory.

Alot of people didn't have any faith in or respect for Michael due to his inexperience. This changed.

You make an important point. We need to remember that in the book, Mike was viewed as "yellow" or weak by the other Families. Even in the movie, the line "Sollozzo knows he's a civilian" implies that Mike is not in the business, nor is he considered strong enough to be in the business. Why else would Sonny, Tessio & Clemenza all laugh at Michael's suggestion to kill McCluskey & Sollozzo?

The view of Michael (before the Sollozzo murder) is that of a non-factor within the Family. This view is seen by the other Families, as well as Clemenza, Tessio, et. al. With Sonny dead and Vito ailing, the Corleone's were deemed vulnerable by their enemies. No one initially expected much out of Michael when he was given the power. Remember Tessio argued with Michael's decision not to recruit more men: "Mike, you're wrong."

Therefore, the execution of the plan to kill the heads of the Five Families, Moe Green & Carlo was most likely a shock to the mob underworld. Obviously, they all knew who had ordered the killings since Michael was still alive. I think that they greatly underestimated his cunning & planning and realized that he was as intelligent (or maybe moreso) than Vito and that Michael was a forced to be reckoned with.

Yeah I think it's realistic that it would "settle all family business" as no one would dare think of doing anything back to some one who has it in them to wipe them all out.

Cheers for wasting the Long good Friday for me

Speaking of the Long Good Friday-hence the IRA, has anyone else seen the movie "Michael Collins" with Liam Neeson? For those who haven't, Collins was one of the founders of the IRA in the '20's. There is a part where he settles his country's business on a certain night that reminds me of the baptism sequence of GF1 like no other movie i've seen. The movie plays with a few facts but is mostly factual. This part particularly DID happen. GF fans who haven't seen it might want to check it out for this.

Yes it is an excellent film

But we dont KNOW there wasnt any reprisals against Michael just because we didnt see it, and there is the question, how would they know for sure it was corleone? later on they would realise when they see all the other dons dead it must be him, but by then Michael had moved to Nevada. only clemenza was left in NY and you know what happened to him

I would also like to mention that if you remeber when the Don was almost killed Tom said "if we lose the Old Man, we lose have our strenght, out political contacts etc." "if your pop dies sonny, make the deal" I think this was exactly what the other families did, by loseing there dons it was just as damaging as for the Corleones if they had lost Vito