Or, Obama's decision could be a countermove against Russian President Vladimir Putin, because Russia (preceded by the Soviet Union) is a long-time supporter of Cuba and is now being seen as the most formidable geopolitical rival of the US. For example, a little-noticed agreement between Cuba and Russia this July reopened a Soviet-era intelligence base south of Havana. Liberalization may be Obama's way of sticking it to Putin and blunting Moscow's influence on Havana.

And why did Cuba agree to the thaw with the US? Some might call it divine intervention, driven by the efforts of Pope Francis. But there is a much more earthly reason: market forces and the pragmatism of Cuban President Raul Castro.

Cuba's latest patron is Venezuela. The late Venezuelan president Hugo Chavez was a disciple of Fidel Castro and his oil-oriented economy was strong enough to fuel both economies. But under President Nicholas Maduro, Venezuela faces a storm. Oil sales make up 96 percent of Venezuela's foreign currency income, and with the price of oil in free fall, the country's currency has fallen by a third in the past month. No wonder, many Venezuelans are questioning continued aid to Cuba, estimated at $5 to 15 billion a year, or about 15 percent of the Cuban economy.

Many Cubans remember the painful days they call the "Special Period" from 1989 through 1993 when the Soviet Union's long-time support evaporated and the Cuban economy shrunk by 35 percent. Cutting a deal with the US seems to be an insurance against a "Special Period II" for Cuba. The decision will improve US relations with the rest of Americas and the world.

Presidents worry about their place in history. Freed of not having to contest another election, faced with a belligerent Republican Congress, and secure in the notion that he could use both his veto power and ability to issue executive orders to get through, Obama has taken a decision for which he will be most remembered. And that goes for the 83-year-old Cuban president as well.

The author is a senior adviser to Tsinghua University.