Since any normal white person can look around and notice the government, media, educational, banking, and judicial system are completely criminal (occupied by Jews), and civilization is imploding due to this, none of them are expanding anywhere.  Why have a bunch of kids that will just be slaves for Jewish psychopaths?  The only people expanding are 60 IQ negroes, 80 IQ Mexicans, and single mother criminal factories.  

That's one indirect reason civilizations thought the institution of marriage was important in the past.  If you force people to get married to have kids, it limits how much the bad genes can reproduce, since the good, K-selection genes don't have many kids, otherwise you are overwhelmed with trash who attempt to externalize the cost of the kids to society to reproduce out of control.  Without a stable 1:1 institution of marriage, you have things happening like one woman having 5 kids from different fathers who all turn out to be felons, or one guy with crap genes marrying four women with crap genes and having 17 kids with crap genes flooding the world with garbage:

https://www.imdb.com/title/tt1721666/