Not long after the end of World War II, the United States embarked on a major embassy-building program in capitals around the world and used modern architecture to convey America as a progressive, modern nation, unlike the repressive, Communist Soviet Union. Some have called it the battle of the “curtain wall” versus the “Iron Curtain.”

The embassies built during the Cold War were designed by some of the most renowned architects in the world, including Eero Saarinen, Walter Gropius, and Edward Durell Stone. These buildings were not simply a place to apply for a visa or for diplomats to discuss international relations—they also housed agents of the newly formed C.I.A. and were used for cultural diplomacy or “soft power,” with auditoriums, libraries, and art exhibitions where locals could learn more about the benefits of an open, modern America.

These Cold War embassies represent an era when the world admired the values and culture of the United States. American heroes were not just soldiers returning from World War II, but also actors such as John Wayne, jazz musicians like Louis Armstrong, and Abstract Expressionist painters like Mark Rothko and Jackson Pollock. Unfortunately, terrorist attacks at U.S. Embassies in Kenya and Tanzania in 1998, and the World Trade Center attacks in 2001, have made these open, porous buildings obsolete, as they cannot be adequately protected in their dense, urban environments. The new embassies are large, closed, and highly secure compounds.

Of all the Cold War embassies, my favorite is the U.S. Embassy in Havana, designed by Harrison & Abramovitz, who also designed the C.I.A. headquarters, in Langley, Virginia. Havana is one of the earliest Cold War embassies, heavily influenced by the United Nations headquarters (Wallace Harrison was director of planning) and by the International Style—flat roof and façades, extensive use of glass, repetitive window design, and lack of ornamentation. The State Department has plans to renovate the aging building, due to the damaging exposure of salt water and high winds.

The building’s political dynamics continue to be front-page news. Not long after the Castro revolution overthrew Batista and weeks before John F. Kennedy’s 1961 inaugural address, the embassy was closed and overseen by the Swiss government for decades. Obama reopened the embassy in 2015, but the building has been effectively closed until recently, due to alleged sonic attacks that cause severe cerebral issues, now called “Havana syndrome.” Russia has denied any involvement.

Unfortunately, many of the embassies built during the height of the Cold War (1948–62) have been decommissioned and sold when they were most needed. Both of Eero Saarinen’s embassies have recently been sold: London, sold to a Qatari investment fund, was gutted and will become a high-end hotel designed by David Chipperfield, while Oslo was purchased by a private investor and is protected by historic-preservation laws.

We have entered a new Cold War with Russia’s invasion of Ukraine and watch anxiously as China appears prepared to invade Taiwan. Putin’s threat to use tactical nuclear weapons in Ukraine is a stark reminder of the near nuclear exchange between the U.S. and the U.S.S.R. in October 1962 (the Cuban missile crisis). Let’s hope Biden has the diplomatic wisdom J.F.K. did during that crisis to convince Putin, via back channels, to avoid the use of nuclear weapons.

As the U.S. Embassies of the Cold War fade into history, my hope is that we appreciate their significance and the context in which they were built. Although historic preservation is an important cultural component in many parts of the world, it’s not so in the United States. Saving buildings, particularly those with historical, cultural, or architectural significance, is important as a reminder of our history.

We have also learned that re-purposing buildings makes enormous environmental sense, given the embedded energy in those buildings and the energy required to build new ones. If new, highly secure embassies are to be built, I am encouraged by the State Department’s renewed focus on architectural design. One of the best U.S. architects working today, Jeanne Gang, has designed the new U.S. Embassy in Brasília. Let’s hope the U.S. is, once again, creating embassies that reflect an open, free, and progressive nation.

David B. Peterson is C.E.O. of Onera Group, Inc., and is the executive director of the Onera Foundation, a private foundation dedicated to supporting historic preservation and the education of students from primary school through middle school. His first book, U.S. Embassies of the Cold War: The Architecture of Democracy, Diplomacy and Defense, will be published on September 19