Discussion about population as a form of commodified labour-power is rare. There is an interplay between the law of value and population. Since, labour is commodified in capitalism this means that the maximum productive population in a country is a given from their level of division of labour and constant capital, the people exceeding this number were called surplus population by marx. Certainly, in the modern era capitalist states are compelled to control this surplus,  either directly or not. in the case of neoliberal states the plan is indirect, taking the form of regulation to the labour market. Although in some countries like China and Japan the plan is explict and formulated with full knowledge. Additionally, this commodification implies that labour is subject to crisis, like other commodities are.

Engels seemed to think this is the case, for in his 1844 essay "Outlines of a Critique of Political Economy" he decries the degradation of man into surplus population, he even points out how Mathus' insights on population were a call for bourgeois population control on those times of crisis, however he did not go further into the topic. Later, the annonymous author of the article "Auschwitz or the great alibi" talks about this dynamic in the 20th century, in the middle of ww2, his most notable point is that as a crisis of population happens in a big scale sometimes it became useful for a fascist country to plan the death of the surplus population stating "In “normal” times, when it only affects a few, capitalism can leave those people rejected from the production process to perish alone. But in the middle of a war, when it involved millions, this was impossible. Such “disorder” would have paralysed it. It was therefore necessary for capitalism to organise their death", This points to a development, where population began to be controlled explicitly by the state, in the form of a plan.

The true question then becomes, Is explicit population planning just a thing done in times of upheaval? I would argue that it isn't, it is rather a tool increasingly used by states in the modern era. The biggest and most explicit example is China under the one child policy, through which population targets are met, and when targets need to increase the policy is changed accordingly, from one child to two children in recent times. Additionally, the other tool i would cynically argue is used in this way is abortion, and access to contraceptives, of course both of those have changing regulations, with them sometimes being widely avalible, and at other times being restricted, this depends of the government in power. However, as government the "embodiment of the total national capital" like Engels calls it in anti-duhring, they are compelled to keep in mind the opinion of the ruling class, and its different sectors, which will change in accordance to demand of labour, so sometimes they will be compelled to restrict both, and sometimes to make them easier to access. Similarly with state programs to boost births, like the ones present in the nordic countries and Japan, done to boost production of workers. Finally, there is also industrial regulations in general, since constant capital can be created from accumulation, it is possible to increase the employable people by loosening regulations on industry, which can increase surplus labour conversion into capital.

Another major way in which surplus population is controlled is through immigration. Immigration requirements in first world countries tend to favor professions with low surplus populations, like ones that are highly specialized, and require advanced education, these are the people that have an ever increasing demand by the national capital, and which thus can be more or less freely let in without them causing problems associated with a numerous enough surplus population. This system is designed to tighly control low paying, meanial jobs, that despite being highly needed, walk on a tight edge of fluctuating demand, and which accordingly require harder control as to prevent surplus population issues, control which is excercised through extra the legality of illegal immigration (think of this in the same way as this: through history a way of controlling wages to be as small as possible was to pay people less than they could use to eat and using charity to give them the rest). This process of importing people can have a redistributive nature, as countries of origin produce too many highly educated profesionals, which cannot be supported by their meager national capital, although in times of crisis it definitevely takes a parasitic nature, as the price labour-power has to be brough down, and the imperial metropoles start to suck in enough people to do so, even at the cost of countries of origin.

Importing people depends heavily on circulation, and has changed with the gains of the proletariat. Before in victorian times, child labout was allowed, which meant that the fluctuations in demand of labour power could be handled very short term, by just creating another batch of people, as kids could start to work as early as thirteen years, this meant that policies of removing female body autonomy, strict familiar structure, and represion of lgbt minorities tended to be selected for in official policy, and crisis of over production of people could simply be handled by exporting people to colonies, along with some capital, or they could just be left to starve. On the other hand, as proletarian triumphs in child labour laws entered into effect, and as jobs required a higher qualification, simple population control methods as before could not be used, so if population was to be controlled it could only be done through immigration, as it allowed short term control over labour markets, this in itself implies the existence of illegal immigration as a neccesity of the system, given that deportations are the method of controlling the surplus population, and number of illegal immigrants always has to be big enough as to bear the brunt of fluctuations in labour demand. This in itself implies the existence of a set of countries still governed by the old princeples, in it's majority conservative, which cannot attract immigrant labour, and thus have to go by with a constant surplus population, which has to continuosly starve.

This last set of countries tend to control surplus population through the rebirth of home industries, seen in first world countries in some ways but mostly in the third world. Home industries were industries in the victorian era that used backwards processes with low yield and productivity that were made competitive by the use of a hyper exploited labour force, these often worked in uniquely backwards sectors of the economy, or were patches of firms using older production techniques to competed against more advance firms, by the use of underpaid labour-power. Examples of this can be seen in the third world by street vendors, salesmen of unique and native commodities not yet fully integrated into the capitalist mode of production, and which thus cannot be outcompeted by first world firms; another example in the first world would be the abundance of self employed contractors, and independent workers, who could easily reduce cost of circulation and production by centralizing, but don't. These types of jobs are used to store the surplus population, as the bourgeois doesn't really value killing people, and will not go that far unless fully needed, and since labour-power is a commodity, it needs to be taken care of, or at least to the extend that it must be prevented from spoiling, i.e. dying in mass. This is why as much as i love empanadas legislation against these industries is progresive, as it forces them to centralize, and unify the proletariat interests around wage gains.