Havana is the capital city of Cuba, where Michael Corleone went in 1958 to discuss business with Hyman Roth of Miami. In Havana, Michael's vehicle of choice was a Mercury Montclair. At this time, war was raging between the forces of President Batista and revolutionary Fidel Castro.
On New Years Eve, Michael sent his bodyguard Bussetta to kill Roth and his associate Johnny Ola, which failed. Bussetta succeeded at murdering Ola, but he himself got murdered by Cuban soldiers, who were likely aware of the plot and ordered by Batista to thwart the assassination. As a result, Roth's life was spared.
This night also brought down Batista's regime, as he abdicated and fled the country. Michael Corleone also left that night, as did his brother Fredo, who feared for his life after unwittingly betraying his brother.