This effect, to which physical causes give rise in certain Eastern countries, was produced in Greece by the nature of the government. The Greeks were a great nation, composed of cities each of which had its own government and laws. They were no more conquerers than the cities of Switzerland, Holland, and Germany are today ; in each republic the legislator’s objective had been the welfare of the citizens within, and a might without that would not be inferior to that of the neighboring cities.  With a small territory and great felicity, the number of citizens could easily increase and become burdensome ; hence they constantly created colonies ; they sold themselves for war, as the Swiss do today ; they neglected nothing that could prevent the excessive proliferation of children.
There were republics among them of singular constitution. Subjugated peoples were obliged to furnish the subsistence of citizens : the Lacedæmonians were fed by the Helotes, the Cretans by the Periecians, and the Thessalians by the Penestæ. There had to be only a certain number of freemen so that the slaves would be able to furnish their subsistence. We say today that we must limit the number of regular troops ; now Lacedæmon was an army maintained by peasants : therefore that army had to be limited, or else the freemen, who had all the advantages of society, would have proliferated without number, and the laborers would have been overwhelmed.
Greek politicians therefore paid particular attention to regulating the number of citizens. Plato sets it at five thousand forty, and he would have it checked, or propagation be encouraged, according to need, by honors, shame, and warnings by old men  ; he would even regulate the number of marriages,  so that the population can be replenished without the republic being overburdened.
If the law of the country, says Aristotle,  forbids exposing children, then the number each person engenders must be limited. If someone has more children than the number defined by law, he advises  making the woman abort before the fœtus is alive.
The infamous means which the Cretans employed to prevent an excess of children is related by Aristotle, and I felt my modesty alarmed when I set about to relate it. 
There are places, says Aristotle again, where the law confers citizenship on foreigners, or bastards, or those who are merely born of a citizen mother ; but as soon as there are enough people, it no longer does.  The savages of Canada burn prisoners ; but when they have empty cabins to give them, they receive them into their nation.
Sir William Petty has assumed in his calculations that a man in England is worth what he would sell for in Algiers.  That can be valid only for England ; there are countries where a man is worth nothing, and there are some where he is worth less than nothing.