COMMENTARY on 4:90
A. Yusuf Ali:

Translation:
Except those who join a group between whom and you there is a treaty 608 (Of peace), or those who approach 609 you with hearts restraining them from fighting you as well as fighting their own people. If Allah had pleased, He could have given them power over you, and they would have fought you: Therefore if they withdraw from you but fight you not, and (instead) send you (Guarantees of) peace, then Allah Have opened no way for you (to war against them).
Commentary:

608  Except the exception refers to "seize them and slay them", the death penalty for repeated desertion. Even after such desertion, exemption is granted in two cases. One is where the deserter took asylum with a tribe with whom there was a treaty of peace and amity. Presumably such a tribe (even though outside the pale of Islam) might be trusted to keep the man from fighting against the forces of Islam-in the modern phrase, to disarm him and render him harmless. The second case for exemption is where the man from his own heart desires never to take up arms against Islam, though he does not wish to join the forces of Islam, to fight against a hostile tribe (perhaps his own) fighting against Islam. But he must make a real approach, giving guarantees of his sincerity. In the modern phase he would be "on parole". But this provision is much milder than that in modern military codes, which grant the privilege only to enemy prisoners, not to those who have deserted from the army granting them parole. The hypocrites were in that position, but humanity as well as policy treated them with great leniency.

609  Approach or come: refers not to the physical act of coming, but to the mental attitude; the heart is mentioned for sincerity. When they sincerely promise not to fight against you, do not pursue them. Remember that if they had fought against you, your difficulties would have been increased. Their neutrality itself may be a great advantage to you. So long as you are satisfied that they are sincere and their acts support their declarations of peace with you, you should not consider yourself justifed in pursuing them and warring against them.

 

Muhammad Asad:

Translation:
unless it be such [of them] as have ties with people to whom you yourselves are bound by a covenant, or such as come unto you because their hearts shrink from [the thought of] making war either on you or on their own folk - although, if God had willed to make them stronger than you, they would certainly have made war on you. 110 Thus, if they let you be, and do not make war on you, and offer you peace, God does not allow you to harm them. 111
Commentary:
110  Lit., "if God had so willed, He would indeed have given them power over you, whereupon...", etc.- implying that only the lack of requisite power, and not true good will, causes them to refrain from making war on the believers.
111  Lit., "God has given you no way against them": a reference to the ordinance laid down in verse 86 above.