Delmer Berg, the last known living veteran of the Abraham Lincoln Brigade, which vainly fought against Fascism’s advance into Spain in the late 1930s, died on Sunday at his home in Columbia, Calif. He was 100.

His death was confirmed by Marina Garde, the executive director of the Abraham Lincoln Brigade Archives in New York, who said Mr. Berg was believed to have been the only survivor left of the nearly 3,000 quixotic young Americans who volunteered for the Spanish Civil War in a bloody prelude to World War II. About 800 of those who volunteered were believed to have been killed.

Mr. Berg, an unreconstructed Communist, was a 21-year-old union-card-carrying hotel dishwasher in 1937 when he spotted a billboard for the brigade and, through the Young Communist League, enlisted. After cobbling together bus fare to New York, he boarded the French luxury liner Champlain for France.

“I was a worker,” Mr. Berg told The Modesto Bee, a California newspaper, in November. “I was a farmer. I was in support of the Spanish working people, and I wanted to go to Spain to help them.”