Is having a caliph obligatory (fard)?

Most certainly - both the Ahle Sunnat and the Shias have reported through continuing narrations that the Holy Prophet (S) says: "Whoever dies without being bound by the oath of allegiance (bay'ah), dies the death of the time of jahiliyya(pre-islamic times)." (Sahih al-Muslim) "You should stick to the main body of the Muslims and their Imam(leader). " (Sahih al-Muslim) "Whoever died without an Imam he dies a death of jahilyyah(pre-islamic times)." (Musnad Ahmed) Imams used to refer to our political rulers... now it is reduced to a secular old man who leads our collective prayers in state controlled mosqued... Abu Bakr went to a lady from the Ahmas tribe called Zainab bint Al-Muhajir... She said, "How long shall we enjoy this good order (i.e. Islamic religion) which Allah has brought after the period of ignorance?" He said, "You will enjoy it as long as your Imams keep on abiding by its rules and regulations." She asked, "What are the Imams?" He said, "Were there not heads and chiefs of your nation who used to order the people and they used to obey them?" She said, "Yes." He said, "So they (i.e. the Imams) are those whom I meant."(Sahih al-Bukhari) The classical scholarship across the Muslim world had a consensus on the issue and included it in books of creed. Here are some examples: - Nawawi: "They (the scholars) consented that it is an obligation upon the Muslims to appoint a khalifah and that its obligation is by revelation, not reason." - Qurtubi: "This aya is an evidence for the appointment of a Khalifah. He is listened to and obeyed, for the word is united through him and the ahkam (laws) of the khalifah are implemented through him and there is no difference of opinion regarding the obligation of that between the umma, nor between the scholars, except what is narrated from al-Asamm (lit. the deaf), who was indeed deaf with regards to the Shari'a, as were all those held his opinion and who followed it." - Ibn Hazm: "The Imama is a complete authority and general leadership over all the people in all important religious and temporal affairs. Its roles includes the defense of the territory of Dar al-Islam, looking after the interests of the community, establishing the Islamic da'wah by providing evidence and proof and by the sword, restraining deviation and inequity, providing help and support to the oppressed against transgressors and recovering dues from those who refuse to fulfil them and providing them to those who were deprived of them... the companions of the Messenger of Allah (saw) saw that moving swiftly to appoint the imam was the right thing to do; thus they left the preparation of the Prophet's burial because of being engaged in this task, fearing lest a tribulation encompass them." - ibn Taymiyah: "It is imperative to know that the office in charge of governing the people is one of the greatest obligations of the din. Nay, there is no establishment of the din or the dunya except by it... Further, (appointing a leader is obligatory) because Allah has obligated enjoining the good and forbidding the evil and this is not executed except through a power and authority." - Mawardi: "They (scholars of ahl al-sunnahhh) said regarding the khilafah and imama that the Imama is an obligation obligated on the umma to the end of establishing the imam who would appoint for them judges and ministers, secure their frontiers, mobilise their armies, divide the fay' and give justice to the oppressed from the oppressors; and they said that the way of contracting the imama for the umma is by their choice through exertion of effort." - Abdul-Qahir Al-Baghdadi: "All of ahl ul-sunnah agreed, as did all the murji'a, all the Shi'a and all the khawarij upon the obligation of the khilafah and that it is obligatory on the umma to submit to a just imam, who establishes upon them the ahkam of Allah and manages their affairs by the ahkam of the Shari'a with which the Messenger of Allah (saw) came." - Nasafi: "When the death of Abu Bakr (ra) neared he said (to the sahaba), "Consult amongst yourselves about this matter (of khilafah)". He then described the attributes of Umar (praising him) and chose him as successor. It did not occur to his heart, or that of anyone else, in the least, that it is permissible for there to be no imam. When the death of Umar (ra) neared he made the matter one of consultation between six and they consented upon Uthman (ra) and after that upon Ali All of this indicates that the sahaba (ra), the first and best of the Muslims, consented that having an imam was necessary...This type of consensus is a definitive evidence for the obligation of the khilafah." - Haskafi: "Know that it is obligatory for there to be in the jama'a of the Muslims a khalifah for interests that simply cannot be fulfilled except with his presence..." - Shawkani: "The Imams (of the four madhabs: Abu Hanifa, Malik, Shaf'i, Ahmad) - may Allah have mercy on them - all consented that the Imama is an obligation and that the Muslims must appoint an imam who would implement the rites of the din and give the oppressed justice against the oppressors and they agreed that it is not permitted that there be over the Muslims, at any one time, two imams, in agreement or discord and that the imams are from Quraysh and that is permitted for the imam to choose a successor." https://dl.dropboxusercontent.com/u/49875620/Classical_scholars_on_Khilafah.pdf