is a principle of the family systems approach that explains why, for instance, the advent of puberty can result in poorer relationship quality between adolescents and their parents.

Disequilibrium

Explanation:

Disequelibirum is a situation when a cognitive imbalance occurred because we obtain a new set of information that contradicts a pre-existing thought structure that we believed in.

This can explain the behavior that adolescents do when they 'rebeled' to their parents. Before entering adolescents age, we obtain our sense of belief, value, or principles only from the teachings of our parents.

But after we entered adolescents age, we started to obtain a new information about belief, value , or principles from other people in our social group. Often times, this new information will contradict the teaching that the parents thought us. This is what causing the poorer relationship quality between adolescents and the parents.

ever since wwii tmthey always did hated each other.

i believe the answer is:   psychological  experiment

in this experiment, wilhelm wundt became the first person that implement scientific method in analyzing the pyschological phenomenon.

due to this result, wilhelm wundt also able to make psychology to be acknowledged as a separate scientific field from biology.