God of the Bible punishes sin
God punishes nations that are disobedient. God does this by destroying their offspring and reducing their birth rates and their numbers, giving them diseases, misfortunes and wars and conflicts and civil wars to eradicate them.
We can see the examples of nations having very low birth rates, because they are sinning too much. They are dying nations.
"I have seen these people, the Lord said to Moses, and they are a stiff-necked people. Now leave me alone so that my anger may burn against them and that I may destroy them." - Exodus 32:9 to 32:10
"Yet he does not leave the guilty unpunished; he punishes the children and their children for the sin of the parents to the third and fourth generation" - Exodus 34:7
Exodus 34 says that children are punished, possibly destroyed or deformed, for the crimes of their parents.
This is what the Leviticus 26 says about God's punishment:
"I will do this to you: I will bring on you sudden terror, wasting diseases and fever that will destroy your sight and sap your strength. You will plant seed in vain, because your enemies will eat it."
"I will set my face against you so that you will be defeated by your enemies; those who hate you will rule over you, and you will flee even when no one is pursuing you."
"Your strength will be spent in vain, because your soil will not yield its crops, nor will the trees of your land yield their fruit."
"I will send wild animals against you, and they will rob you of your children, destroy your cattle and make you so few in number that your roads will be deserted."
Making a nation few in numbers means to eradicate them by lowering birth rates and making them die to reduce their numbers.
"If in spite of these things you do not accept my correction but continue to be hostile toward me, I myself will be hostile toward you and will afflict you for your sins seven times over. And I will bring the sword on you to avenge the breaking of the covenant."
"Bring the sword" means bring wars and violence to society.
"When I cut off your supply of bread, ten women will be able to bake your bread in one oven, and they will dole out the bread by weight. You will eat, but you will not be satisfied."
"You will perish among the nations; the land of your enemies will devour you. Those of you who are left will waste away in the lands of their enemies because of their sins; also because of their ancestors’ sins they will waste away."
This means how enemies of the nation will outnumber it greatly. God does this by causing wars and civil wars and conflicts and divisions in society.