I believe the answer is: Asian
In united states, Parents from Asian communities tend to put more emphasize on discipline and high expectation on the education of their children.
Because of this, On average Students from Asian Ethnic communities typically have higher scores compared to students from other ethnic community. This positively correlated to the household income of Asian Family. Asian households are the one that have highest household income in United States.
One event is that they did human sacrifice and POW would be killed for it. this could cause a decrease in population
B.) Families no longer form solely through marriage.