Why is the stress on the word 'tribalism' placed on the 1st syllable against the rule of stressing the 2nd syllable at the end of a word that ends with '-ism'?
As the question demonstrates, the English language has rules. Yet, those rules are sometimes inconsistent and can be broken. The rules for pronunciation may be a bit less strict as compared with other languages.
As such, the rules for pronouncing English words are general. The rules will apply most of the time to most types of words. Yet, they may not apply all of the time, meaning that for certain words the general rules do not apply to that particular word.
The pronunciation of the word ‘tribalism’ is an example of this. The root of the word is ‘tribal.’ As a two syllable word, the stress is on the first syllable, ‘tri.’ The stress on the first syllable does not change for the word ‘tribalism.’