Tafsir of Al-Anfal 8:73

{And those who disbelieved are allies of one another}

The apparent meaning is the establishment of alliance between them, just as the Almighty said regarding the Muslims: {Those are allies of one another} (Al-Anfal: 72).

Its meaning is: He forbade the Muslims from allying with those who disbelieved, from inheriting from them, and He made it obligatory to distance themselves and sever ties with them, even if they were relatives. He commanded that they cease inheriting from one another.

Then He said: {Unless you do it}

Meaning: Unless you do what I have commanded you regarding the solidarity of the Muslims and their alliance with one another—even in matters of inheritance—by prioritizing the bond of Islam over the bond of kinship, and unless you sever the ties between yourselves and the disbelievers, and treat their kinship as if it were no kinship at all, then {there will be fitnah (tribulation) in the earth and great corruption}.

This is because as long as the Muslims do not become a single hand against polytheism, polytheism will remain manifest and corruption will increase. (It was also recited as kathīr with a thā’).

{And those who believed, emigrated, and fought in the cause of Allah, and those who gave shelter and aided—it is they who are the believers in truth. For them is forgiveness and a noble provision. And those who believed after, and emigrated, and fought with you—then they are of you. But those of [blood] relationship are more entitled to one another in the Book of Allah. Indeed, Allah is Knowing of all things.}