Halakhah su Deuteronomio 20:16

And this commandment is practiced by males and females in every place, and at all times that we have the power to kill them. And Rambam, may his memory be blessed, wrote (Sefer HaMitzvot LaRambam, Mitzvot Ase 187), "And maybe someone will think that this is a commandment that is not practiced throughout the generations, since the seven nations have already been destroyed. However this will [only] be thought by someone who does not understand the matter of what is [considered] practiced throughout the generations and not practiced throughout the generations." And the major principle from his words, may his memory be blessed, is that you need to know that any commandment the performance of which has disappeared because its time has passed - such as the commandments that they had in the wilderness, but not afterwards in the Land; and so [too,] the commandment of apportioning the inheritance which was only for the generation that was [present] for the division of the land upon their entrance into the Land - those like these are the ones that are called, 'not practiced throughout the generations.' But all of the commandments that have disappeared from us because it is not found among us that we can do it - but not because the verse makes its dependent on a specific time, such as the this one of the destruction of the seven nations and Amalek in each and every generation that we find them, and even though we have already done to them that which we are obligated through our King David, who destroyed them to the point that there only remain a small number of them that have scattered and been diluted among the nations until their memory is not known, and it is not even in our [power] now to pursue them and to kill them - nonetheless, this commandment is not called because of this a 'commandment that is not practiced [throughout the generations].' And understand this principle and hold on to it. And one who transgresses this, and one of them comes to his hand - and he is able to kill him without endangering himself through the matter - and he does not kill him, has violated this positive commandment, besides that he violated a negative commandment which is stated about them (Deuteronomy 20:16), "You shall not keep any soul alive," as we will write at the end of the Order of Shoftim with God's help about the commandment not to keep alive one from all of the seven nations (Sefer HaChinukh 528).

To not keep alive a soul of the seven nations: That we were warned with a negative commandment not to keep anyone of the seven nations alive in every place that we find them and are able to kill them without danger to our souls. And the seven nations are the Canaanite, the Perizite, the Hivite, the Jebusite, the Hittite, the Girgashite and the Amorite. An about them is it stated (Deuteronomy 20:16), "you shall not keep a soul alive." And even though the truth is that King David killed many of them to the point that he almost finished them [off] and destroyed their memory, nonetheless a few of them remained that assimilated among the [other] nations. And anyone who finds some of them is obligated to destroy them in every place that they are. And I have written all of the content of this commandment at length above in the Order of Ve'etchanan on the commandment of killing the seven nations (Sefer HaChinukh 525). And [so] take it from there.