The pre-War flag of the Republic of Ireland.
The Republic of Ireland (Irish: Poblacht na hÉireann) was a pre-War country in western Europe.
No details are known about the state of the Republic of Ireland after the Great War.
But considering that the Irish republic flag is found multiple times in the Commonwealth, a flag which, while was created in 1830, didn't enter common usage until Ireland became independent in 1922 and later became a republic. This strongly suggests Ireland did form a republic in Fallout's divergent timeline.
Ireland in Fallout
- Colin Moriarty and Moriarty senior originated in Ireland but when Colin was a child they immigrated to the former United States.
- John L. Sullivan is of Irish descent, has knowledge of Irish folk lore, and has an Irish accent.
- Patrick the Celt is descended from Americanized Celts and keeps his heritage alive by collects clothing, food, stories, songs, and knowledge of celtic history. He knows the Irish song Na Gheala Mbeadh (Which is very poor Irish for "The Light Would". Possibly a mistranslation of 'Mo Ghile Mear' 'My Gallant Darling'). 
- Dunwick's Irish Red was an Irish red ale manufactured and distilled by the Dunwik company prior to the Great War. It can't be found in any game; however, the logo for it can be found on beer taps across the Mojave Wasteland.
- In 1897 Irish engineer John Philip Holland created the Modern submarine design.
- In 1847 group of Irish volunteers, including U.S. Army deserters, joined the Mexican side in the Mexican–American War. These soldiers, known as Los San Patricios or Saint Patrick's Battalion.
- In the underpass near the Nipton Road reststop there is a piece of graffiti which states "The centre cannot hold", a quote from the Irish poet WB Yeat's poem "The Second Coming."
- Exploration Database, Megaton: "Megaton
A town built around an undetonated atomic bomb. My kind of place!
Megaton is pretty well fortified now, but back in my day it was even more ramshackle. Great place to grab a drink or a broad.
I hear Moriarty even has his own place now. Guess that shouldn't surprise me. That guy had been playing the angles since the day he ended up in this country, as a kid."
- Fallout 3 Official Game Guide Game of the Year Edition p.66: "Colin Moriarty
Moriarty, 50, has been here nearly his entire life. He claims that his grandfather helped found the original settlement a few years after the war. His father used the nearby trade routes to amass wealth, which is used to help secure Megaton. Colin inherited this wealth when his father was killed during a Raider attack when Colin was 14. Colin's first move was to build a fence around the town. Since then, the people have looked to Colin as a benefactor despite his running drinks, Chems, girls, and games out of his saloon. Simms turns a blind eye to Moriarty's activities, because he is acutely aware that the town needs Colin's support and resources."
(Fallout 3 Official Game Guide Game of the Year Edition Wasteland Census)
- Fallout Bible 9