Over more than two decades, Jean-Noel Frydman built France.com into a thriving business, selling tours online to Paris, Burgundy, the Riviera and other popular French destinations.

But on March 12, his business vanished.

That was the day the French government prevailed in a yearslong effort to seize the coveted domain name, persuading the company that had long managed it, Web.com, to hand it over.

“It was a shock to have everything that I’ve worked on for almost 25 years get destroyed overnight,” said Mr. Frydman, who was born in France and is a dual French-American citizen. “In one minute, it’s all gone, without any kind of heads up.”

Now, Mr. Frydman, who says he stands to lose millions of dollars in profit without the site, is fighting back — by taking France to court in America.