But nearly 20 years after the U.S and Vietnam buried a bloody hatchet, an American venture capitalist based in Hanoi has an another theory about the length of time it took for the Western Hemisphere enemies to begin normalizing relations.

"I'm wondering if it took so long because there was never a war," said Phuc Tran, who was born in Vietnam, left as a young refugee in 1975 and returned in 2000 as a representative for Intel.

The American War, as it's known here, left a great wound that demanded healing, Tran said, while the U.S. and Cuba nurtured enmity for political reasons. "For guys like John McCain and John Kerry, Vietnam was personal. With Cuba, you don't have a McCain and Kerry to drive change." The Republican U.S. senator from Arizona and the secretary of state served in the military during the Vietnam War, and McCain was held prisoner and tortured by the North Vietnamese.

Whatever the reasons, Tran and other observers say the normalization of U.S.-Vietnam relations since 1995 should encourage Cubans and Americans to follow through on President Barack Obama's bid for a new relationship.

Better ties, they say, figure to have palpable economic and social benefits for Cubans and Americans. Commerce with the United States has helped millions of Vietnamese enjoy a higher standard of living, and travel between the countries has soared.

But the Vietnam experience also shows that improved relations with the U.S. may have less of an impact on the ruling regime's authoritarian ways.