It was Fenian Brotherhood and their oath: “labor with earnest zeal for the liberation of Ireland from the yoke of England.” It took General Meade from Eastport, ME; Buffalo, NY; St, Albans, VT as well as using the USS Michigan on Lake Erie to ensure the Fenians should not receive any reinforcements from the U.S. side in their skirmish with Canada.
grant and meade and fenian raids in 1866
http://www.acsu.buffalo.edu/~dbertuca/155/FenianRaid.html
bonus:
Answer:
Brig Gen Dudley McIver DuBose assumed command of the brigade previously known as Wofford’s. Prior to his promotion, he was Col of the 15th Georgia. wiki/Dudley_M._DuBose
His father-in-law was
Brig Gen Robert Augustus Toombs; previously U.S. Senator from Georgia (1853-61); delegate to Georgia secession convention (1861); Delegate to the Confederate Provisional Congress (1861-62); Confederate Secretary of State (1861).
Edit - I can understand why a number of players found the wording of the question confusing and were uncertain as to whether the question was asking for the name of the group in rebellion or the name of the military organization Meade commanded in opposition to that rebellion. For that reason, I am accepting Military Division of the Atlantic as a correct answer.
While Meade later went on to command both the Department of the East and the Third Military District, those commands came to him more than a year after either his last Civil War battle, which took place in April 1865, or his assuming command of the Military Division of the Atlantic, which took place in June 1865. And I can't find any reference to Meade needing to oppose a rebellion while he was in command of either the Department of the East or the Third Military Division. Therefore, I'm not accepting those answers as correct.
Incidentally, I read through the article to which the official answer provides a link, three times, and I could not find any mention of Meade or Grant in it.
hoosier