Fifty-four years ago, the United States broke diplomatic relations with Cuba, and three young Marine guards completed a final duty in Havana: lowering their country's flag before returning home.

On Friday, US Secretary of State John Kerry watched as those same three Marines – Larry Morris, Mike East and Jim Tracy – helped raise the flag once again over the newly re-opened U.S. Embassy.

"It is an approach based on the ties that bind our people, the interests shared by our governments, and the mutual respect that should characterize relations between two proud nations – even when our policies collide," said Kerry in a blog post written on his flight to Cuba.

Three weeks ago, the two nations reestablished formal relations and a Cuban embassy was reopened in Washington, DC.

"In Cuba and throughout Latin America, we are seeing the diplomatic benefits of reversing a policy that divided us from the Cuban people and isolated us in the hemisphere and the world," he explained.

"Whether we are working to prevent oil spills off the coast of Florida, interdict narcotics flows in the Caribbean, or champion democratic values, an engaged America will be a stronger and more influential America."

Though the two governments remain deeply divided, visitors are flocking to the island now, many of them Cuban-Americans, bringing valuable tourism dollars. Airbnb rentals are providing income directly to Cuban homeowners.

"They are supporting self-employed entrepreneurs, the fastest-growing sector of Cuba's economy, some half a million strong, who will be so important to the country's future," added Kerry.

Two decades ago, Kerry also helped normalize relations with another of America's former foes, Vietnam. He believes the same benefits that flowed to that Asian country will eventually transfer to the Cuban people.

"Last week, I returned to Vietnam to find a country that is market-oriented, economically vibrant and friendly to the United States. Its people are also freer — with greater access to information and more autonomy over their lives."

(WATCH a inspiring video about the 3 Marines below, or READ Kerry's post, Why I'm Going to Havana)