History, courage, mentality. Everything. The criteria for martial races was I think; 1) their lifestyle should be active and sporty in general rather than sedentary(i'e hunting etc). 2) their homeland should be hilly preferably 3) history of resistance 4) physique.
No one chooses the warring lifestyle. Some tribes were unlucky to be at the crossroads of invading armies and had no other option but to fight, it doesn't make them "martial". Its a chicken and egg story. Was it the situation that made them "warlike" or were they "warlike" to begin with which put them in such situations!
As for French and Scotts, French are an independent people, Scots not so much?