Approximately 2,800 American volunteers served in the Spanish Civil War on the Republican side. Confirmed indicates that I have two or more sources that place the volunteer in Spain. Those that are confirmed make up “Category I.” Category I includes both those who died in Spain and those who returned. Some of the volunteers identified as Americans are also listed on other nationality lists based on their place of birth or ethnicity. Biographical entries of Category I volunteers are listed on the ALBA website.

“Category II” volunteers lived in United States at some point prior to the Spanish Civil War, but who were neither living in the United States nor American citizens when they went to Spain. [I swapped the definition for Category II & III as they flowAnyone who's been online Sunday probably knows it's Star Wars Day, one of the Internet's favorite holidays, during which fans and nerds alike love to say "May the fourth be with you."

Not only are phrases related to the day dominating the majority of trending hashtags on Twitter, brands are capitalizing on it, too. We've seen Major League Baseball players wielding glowing lightsabers, and Nissan getting punny with its new Juke ad. What's more, musicians such as Chris Daughtry and Ben Folds have teamed up with College Humor in a Star Wars-themed parody.

SEE ALSO: 'SNL' Hilariously Shows What Happens If You Mess With Beyonce

The phrase, "May the fourth be with you" has its roots in advertising. First used on May 4, 1979, Margaret Thatcher's political party placed it in