St. Alphonsus, vol. 2 lib. 6 tract. 5 de matrimonio
(p. 687 (https://archive.org/details/theologiamoralis02ligu_0/page/687/mode/2up)), addressing question "938. Marrieds per se
are bound to render (the debt) and sometimes even to exact (the debt).":
Quote1. Neither is bound, speaking per se, to exact the debt, even if per accidens he is sometimes bound to, either out of charity (e.g., to avert the immanent danger of incontinence of the spouse.) ... or out of legal justice, in which which public health (salus publica) is endangered without the birth of children.Integralism
(https://isidore.co/calibre/#panel=book_details&book_id=7822) ref:10.15: "where populations are declining or threaten to decline, the civil power may offer inducements
to married couples to have children."
Does St. Alphonsus go further, arguing that the State can force
marrieds to have children?
It looks like that a state could force married couples by law to have children in extreme situations where there is immanent or potential danger of a nation falling away through depopulation as we have been seeing lately in many cases.
I remember Bp. Williamson saying something years ago something along the lines of if you don't have children, you lose your country, in reference I think to the state of countries in Europe and in relation to the immigration to there from the Middle East and Africa.