Socially, it has to be Johnson - Jeffries. I've read accounts where various cities across the US broke into riots after the fight, with lynching becoming widespread. It was probably the most important fight of all time. The sheer hatred (mostly white against black) is mind-boggling. I get the impression every person in the country was eager to see the fight, and no-one would be sitting on the fence
Does it get more International than Louis-Schmeling II? We all know what it meant at the time, perhaps what stands out for me is how Louis became the first American/Western World bona fide hero not to be of Caucasian race. Of course there were other African American athletes of the time, Jessie Owens at the Munich Olympics. But none before were embraced like Louis was prior to this fight or in the aftermath. There are so many tales to tell from just one boxing contest.
In terms of signifigance,I'd take the 'Thrilla In Manilla' out of the frame. It was indeed a great fight,but very few actually forecasted it as being so beforehand. Johnson-Jeffries,because of the disgusting racist climate of the times was very signifigant. Ali-Frazier I was built up as a great fight between two undefeated fighters,and both men had claims on being the real champion at the time. There were also political overtones to it. Louis-Scmelling II was signifigant owing to the Nazi threat,and even many racist Americans put their bigotry aside to line up behind Louis. And the winner is..................................Louis - Schmelling. Purely because World War II increased it's signifigance.
a) Importance to boxing, and b) Social and civic importance? to boxing probably frazier/ali I but on a world level it has to be the louis/Schmelling rematch
From a purely 'FIGHT' aspect,that's dead right,Hook. Massive build up,and the event matched the hype.
In terms of importance in the whole world is Frazier vs Ali I......Definitely Louis vs Schmeling II is up there..... Jeffries vs Johnson probably didn´t a big impact outside of US.....
How on earth is the Johnson vs. Jeffries fight not No.1... let alone no.3 right now. It isn't even close imo and the Johnson vs. Jeffries fight was and still is the ONLY fight of the century.