Baptism By Fire

The Baptism By Fire was the final act in the The Five Families Mob War, which saw a complete victory for the Corleone family.

History
After a sit-down in 2010, Vito Corleone vowed that he would not avenge the death of his son, Sonny, to provide an end to the bitter war.

However, his son Michael, who had just returned from Sicily, took the burden upon himself to eliminate the rival families, without breaking Vito's vow.

Events
Michael, as an father, stood father to Oliver Corleone, his son. As he read out the vows, the murders took place.

William Stracci
William was on his way to a meeting, when he was killed with a pipe in an elevator along with his associate by Pete Clemenza and Charlie Trapani.

Phillip Cuneo
A few minutes later, Phillip Cuneo was at an hotel. Cuneo was aware that Corleone agent Willie Sissy along with Trapani had entered the hotel, but trapped Cuneo in the stairwell, before shooting him ten times.

Sammy Tattaglia
Unlike the other Dons, Sammy was less concerned with matters of business, and was enjoying time with a hooker in a St. Sebastian's Hotel, Crazy Town, when he was gunned down by Charlie.

Emilio Barzini
The Wolf had arranged to ambush and kill Michael Corleone through his hitman Alberto La Ruso, but Alberto didn't have the guts to do it. Barzini had just returned from the Justice Building, and was making his way down the street, before he was assasinated by Charlie.

Trivia

 * This is the last mission in The Godfather Game.
 * There is video of cutscenes on the Wiki.

Would you also kill the other 4 Families Don's if you were Michael? Nah, got better things to do, beside, we just made peace Absolutely Only Barzini and Stracci Only Tattaglia and Cuneo