Very little in the way of shifting in Strength based on where an individual was from ... Lowest average strength is at 26 from Tarabon and the highest average strength (16) hailing from Far Madding, of course the sample size by nation has rather large swings so not a lot to go on really, and some samples are obviously skewed, such as the Sea Folk, who for the most part we only saw the very strong women or had limited strength listings such as the Seanchan. But to be honest I was rather surprised that for the most part strength didn't vary much by nationality, with only a 10-level swing.
Far Madding, 5 listings, 16 Average strength
Sea Folk, 17 listings, 17 Average strength
Amadicia, 5 listings, 19 Average strength
Ghealdan, 6 listings, 19 Average strength
Mayene, 2 listings, 19 Average strength
Aiel, 23 listings, 20 Average strength
Murandy, 12 listings, 20 Average strength
Kandor, 13 listings, 21 Average strength
Andor, 32 listings, 22 Average strength
Saldaea, 13 listings, 22 Average strength
Altara, 8 listings, 23 Average strength
Arafel, 16 listings, 23 Average strength
Tear, 10 listings, 23 Average strength
Cairhien, 11 listings, 24 Average strength
Domani, 12 listings, 24 Average strength
Illian, 11 listings, 24 Average strength
Shienar, 6 listings, 25 Average strength
Tarabon, 17 listings, 26 Average strength