Question

why it is necessary to co-operate with each other to remain United in the society

Answer 1

For a society cooperation is a must. A society is nothing without cooperation and true is that there won't be any society if there isn't any cooperation.

We Humans have it as our nature to cooperate and live together since ancient times. Without this cooperative nature it could never have been possible to form the socities we all have now.

For forming a society the smallest unit is a man and a woman and the smallest institution is marriage. Without cooperation even marriage isn't possible. The whole society starts with the institution of marriage.

If we don't stay cooperatively in a society, then it no longer will be a society, it will all break down into fragments and smaller sections like tribes not a complete society.