“Al-hilf” in the language is the covenant and friendship. It is said “halifuhu” from “’ahiduhu” (he covenanted with him). Except that the word “al-hilf” is used because a technical definition as it is mostly used for military alliance specifically. Military alliances are the alliances contracted between two or more States which make their armies fight together with a common enemy, or make military information or war tools exchangeable between them, or if one of them enters into war they will consult with each other to enter war together or not according to the interests they see. These alliances could be dual treaties contracted between two or three or more States, but they do not consider aggression upon one of the States an aggression against all of them; rather if aggression occurs upon one of the treaty States, the State upon which aggression occurrs, the States with which it has a military alliance and in the light of their benefit they would announce war together with the State facing aggression against the aggressor State or not. And these alliances could be collective alliances in which it is considered that aggression against one of the treaty States an aggression against all of them, so that if there occurs war between one of them with any State then all other treaty States will enter into the situation of war with this State. All of these alliances, whether they were dual or collective or other than that, necessitate that the army fights with its ally to protect it and its entity whether there were numerous leaders or a single leader.

These alliances are void from their basis and are not contracted legitimately. So the Ummah is not obliged with them even if the Muslims’ Khalifah contracted them as it contradicts the Shar’a since it would make the Muslim fight under a Kafir authority and under a kufr banner, and makes him fight in order to preserve a kufr entity; all this is haram. It is not allowed for a Muslim to fight except under Muslim leadership and under the Islamic banner. There came a prohibition in the sahih hadith against fighting under the disbelievers’ banner and their authority, Ahmad and An-Nisa’i narrated from Anas who said: The Messenger of Allah (saw) said:

I.e. do not make the polytheists’ fire a light for you. The fire is an allusion for war; it is said the “fire of war was kindled” i.e. its evil and violent excitement was called into existence. And the fire of fright is a fire the Arabs in jahiliyyah would kindle during alliance. The hadith alludes to war with polytheists and adopting their banner, so the prohibition of war together with polytheists is understood from it.

Alliances would also make the disbelievers fight with Muslims while preserving their entity i.e. they would fight as a State and not as individuals. The Messenger (saw) prohibited seeking assistance of the disbelievers as an entity. It came in the hadith of Adh-Dhihak (ra)

The Messenger (saw) rejected assistance of the Jews and said in a general fashion:

One should not say that we seek assistance from disbelievers upon our enemy and seeking assistance with the disbeliever is allowed since the Messenger (saw) consented to Quzman fighting together with him in Uhud and he was a disbeliever, and accepted assistance from some people of the Jews of Khayber in war; one should not say that because seeking assistance with disbelievers is allowed if they are individuals under the Muslims’ banner. Those whom the Messenger (saw) sought assistance from, he sought assistance from them and they were individuals. Accordingly when Banu Qaynuqa came and they came while they were a tribe with their own leader, and they were like a State who previously made a treaty with the Messenger (saw). They came to fight with the Messenger (saw) and they were upon this situation and it was said to him:

So he refused to seek assistance from them due to this. Accordingly it is not allowed to seek assistance from a kafir army and under the banner of their disbelieving States. Imam As-Sarakhsi said in ‘Al-Mabsut’ in the book of ‘Siyar’: “From the hadith of Adh-Dhahabi (ra)

Its interpretation is that they were powerful in themselves not fighting under the Muslims’ banner. For us, we only seek assistance from them if they were fighting under the Muslims’ banner whereas if they come isolated with their own banner then we do not seek assistance from them. This is the interpretation of what was narrated from the Prophet (saw) when he said:

Narrated by Ahmad and An-Nisa’i via the way of Anas and he said:

This means the Muslim who is under the polytheists’ banner. From this it became clear that a military alliance with disbelieving States is haram in the Shar’a so it is not contracted. It is not allowed for the Messenger (saw) to shed his blood in the way of defending the belligerent disbeliever. Rather the Muslim only fights people so that they enter into Islam from disbelief (kufr). As for fighting disbelievers to enter from kufr into kufr and to shed his blood for that, this is haram.