The Muslims are obliged to live in one state, and be ruled by one Khaleefah. It is forbidden for the Muslims in the world to have more than one state and more than one Khaleefah.
It is also necessary that the ruling system in the Khilafah State be a system of unity, and forbidden to be a system of union (federation of states).
This is due to what Muslim narrated that ‘Abdullah ibn ‘Amru ibn al- ’Aas said that He heard the Messenger of Allah (pbuh) say:
“Whoever pledged allegiance to an Imam giving him the clasp of his hand and the fruit of his heart, He should obey him as long as He can, and if another comes to dispute with him, you must strike the neck of the latter.” It has also been narrated by Muslim that Arfajah said: “I heard the Messenger of Allah (pbuh) say:
‘Whoever comes to you while your affair has been united over one man, intending to divide your power or dissolve your unity, kill him.’” Muslim has also reported it from Abu S’aid Al Khudri that the Messenger of Allah (pbuh) said:
“If the Oath of Allegiance (Bay’ah) has been taken for two Khulafaa’, kill the latter of them.” Muslim reported that Abu Hazim said: “I accompanied Abu Hurayra for five years and heard him talking about the Messenger of Allah (pbuh).
He said: ‘The children of Israel have been governed by Prophets; whenever a Prophet died another Prophet succeeded him; but there will be no prophet after me. There will soon be Khulafaa’ and they will number many’, they asked, ‘what then do you order us?’ He (pbuh) said, ‘Fulfil allegiance to them one after the other, and give them their dues; for verily Allah will ask them about what He entrusted them with.’” The first Hadith demonstrates that if the Imamah (Khilafah) has been given to someone He should be obeyed, and if another man comes to dispute his authority, He should be fought and killed if He did not withdraw the claim.
The second Hadith demonstrates that when the Muslims are united under the leadership of one Ameer, and a person comes along with intent to divide their power and dissolve their unity, his killing becomes compulsory. The two Ahadith clearly indicate prohibition of dismembering the state, and strong warning against its division, and preventing any breakaway attempt even by using the sword (force).
The third Hadith indicates that in the case of the absence of a Khaleefah, due to his death, removal or resignation, then if the Bay’ah has been taken for two Khulafaa’, the latter of them should be killed, and the more so if they were more than two. This clearly demonstrates that the dismembering of the state is forbidden, which means that turning it into many states is forbidden, rather it must remain one single state.
The fourth Hadith indicates that the Khulafaa’ would number many after the Messenger of Allah (pbuh).When the Sahabah asked him about what He ordered them to do when the Khulafaa’ numbered many, He replied that they should fulfil their allegiance to the Khulafaa’ one after the other. They start by the first one they gave their Bay’ah to, for He would be the legitimate one and He alone should be obeyed. As for the others, they are not to be obeyed for their Bay’ah is null and void as well as unlawful. This is because it is forbidden for another Khaleefah to be given a Bay’ah while there exists a Khaleefah already in office. This Hadith also indicates that obedience to a single Khaleefah is obligatory. Therefore it is forbidden for the Muslims to have more than one Khaleefah and more than one single state.