Michael Corleone is visiting Cuba during the New Year’s Eve celebrations in The Godfather Part II.
The Havana storyline takes place in late 1958, as Michael explores business opportunities with the Batista government and organized-crime figures. The celebrations occur while the Cuban Revolution is reaching its decisive stage.
Michael’s plans collapse when revolutionary forces enter Havana on New Year’s Eve. The sudden political upheaval exposes the instability of the proposed business arrangement and helps trigger his return to the United States.
This answer is different from the specific city, Havana, which is the setting of Michael’s stay. Cuba identifies the country, while Havana identifies its capital. The sequence is also distinct from the Lake Tahoe storyline, which takes place at Michael’s Nevada compound.