Wolff was the last commander of the Lincoln Battalion, a unit of American volunteers who fought for the Republicans in the Spanish Civil War. He took the position after the previous commander, Robert Hale Merriman, was killed.
The only US war he participated in was World War II, where he fought the Nazis on the Western Front.
Despite being in his 50s at the time, during the Vietnam War, he offered the service of himself and the other Lincoln Battalion veterans to Ho Chi Minh (Uncle Ho declined). After that, he became an anti-Apartheid activist as well as raising money for the Sandinistas.
I'd recommend commemorating types like these on their birthdays, death anniversaries, etc, instead of some yankie patriot holiday
I prefer to think of it as seizing the holiday for the proletariat