Question

Why there are more federal countries in the world?

Answer 1

 there are more federal countries in the world because it s the best form of government , it keeps people happy, people can rule them selves

it gives people many options , provides then the room to correct their mistakes etc 

many countries are struggling to be democratic

Answer 2

Federal governments are best used in large countries where there exists a diverse group of people with diverse needs but a common culture that unites them together. federal governments help address the wide variety of needs of a geographically large country.
example :Argentina (23 provinces and 1 autonomous city)