The heirs of Nazi-era Jewish art dealers have spent nearly a decade trying to persuade German officials to return a collection of medieval relics valued at more than $250 million.

But they didn't make much headway until they filed a lawsuit in an American court.

The relatives won a round last week when a federal judge ruled that Germany can be sued in the United States over claims the so-called Guelph Treasure was sold under duress in 1935.

It's the first time a court has required Germany to defend itself in the U.S. against charges of looted Nazi art, and experts say it could encourage other descendants of people who suffered during the Holocaust to pursue claims in court.

The case also is among the first affected by a law passed in Congress last year that makes it easier for heirs of victims of Nazi Germany to sue over confiscated art.

"It open all kinds of other claims based on forced sales in Nazi Germany to jurisdiction in U.S. courts if the facts support it," said Nicholas O'Donnell, an attorney representing the heirs.

The collection includes gold crosses studded with gems, ornate silverwork and other relics that once belonged to Prussian aristocrats. The heirs of the art dealers — Jed Leiber, Gerald Stiebel, and Alan Philipp — say their relatives were forced to sell the relics in a coerced transaction for a fraction of its market value.

The consortium of dealers from Frankfurt had purchased the collection in 1929 from the Duke of Brunswick. They had managed to sell about half of the pieces to museums and collectors, but the remaining works were sold in 1935 to the state of Prussia, which at the time was governed by Nazi leader Hermann Goering.

Following the sale, Goering presented the works as a gift to Adolf Hitler, according to court documents. The collection has been on display in Berlin since the early 1960s and is considered the largest collection of German church treasure in public hands.

German officials claim the sale was voluntary and say the low price was a product of the Great Depression and the collapse of Germany's market for art. In 2014, a special German commission set up to review disputed restitution cases concluded it was not a forced sale due to persecution and recommended the collection stay at the Berlin museum.