I grew up hearing their stories: The Viet Cong dominated dinner table conversations. My father talked about jumping into a mortar pit full of scorpions and described sleeping on the roof so he would be the first to spot anything incoming. My mother recounted frantically packing five dresses and pretending to be engaged to an American family friend to secure her last-minute escape to a refugee camp in Guam.

The fall of Saigon was a tragedy—lives lost, a country fractured, families like mine clinging to helicopters or braving the seas. Their exodus reminds us of the lengths people will go to escape the scourge of communism and build something from nothing.

Look at Little Saigon in Westminster, Calif.—the largest Vietnamese population outside Vietnam—or at Eden Center in Falls Church, Va. These are hubs of small businesses born from resilience and extraordinary tenacity. More than 300,000 businesses in the U.S. are owned by Vietnamese-Americans, including the billion-dollar company that makes Sriracha hot sauce. Fifty-five percent of U.S.-born Vietnamese-Americans hold bachelor’s degrees or higher, well above the national average of 38%.

Young Americans today have known peace for decades. But from Saigon to Kabul, we’ve seen how freedom’s promise can vanish in an instant. With distance comes danger: the fading of memory. On this anniversary, we must remember that the gifts of the U.S. are fragile, precious and worth defending.

Americans’ most powerful adversary is now communist China—the same regime that bankrolled and armed the Viet Cong—and we face a different kind of battlefield. National power is no longer measured by military strength alone. It’s exercised through economic leverage, technological dominance and strategic investment. Our freedom is being tested not only in war rooms but in boardrooms. It’s being shaped not only by soldiers but by the choices of everyday social-media users.

So how do we preserve it? Can we give up TikTok, knowing its ties to a totalitarian regime? Will we invest in building the next generation of trusted technology—designed not only to win markets but to uphold freedom?

My father often repeated a simple Seabee motto: “Can Do.” Fifty years after Black April, as new threats challenge liberty, that same spirit must guide Americans to meet this moment.

Ms. Giuda is CEO of the Krach Institute for Tech Diplomacy at Purdue. She served as assistant secretary of state for global public affairs, 2018-20.