Islam is the deen revealed by Allah (SWT) to His Messenger Muhammad (SAW) in order to regulate the life of all human beings on earth – Muslims and non-Muslims – in the correct manner. The thoughts and rules brought by Islam to guide the spiritual, social, economic and political affairs of man is the Islamic shari'ah. It is clear that the ruling system (i.e. the state) plays the most important role in implementing the rules and the way of life of any ideology. Without a state the rules are never implemented in life's affairs. Therefore we find that Muhammad (SAW) and his sahaba (ra) struggled thirteen years in Mecca and then made the hijra to Medina to establish the first Islamic state. After the establishment of the state in Medina the Islamic thoughts and rules started to be implemented in life's affairs. As a result, at first the divided tribes in Medina and later those in entire Arabia became united as one single Ummah i.e. the Islamic Ummah. Muhammad (SAW) himself was the first head of state of the Islamic state and after his death Abu Bakr (ra) was appointed by the Muslims as the Khaleefah. Since then the Islamic state became known as the KHILAFAH state.
The KHILAFAH state is the leadership over the Muslims through which the Islamic shari'ah is implemented in society and the Islamic daw'ah is carried to mankind. In the KHILAFAH state the Muslims appoint a Khaleefah and give him the bay'ah upon the condition that he will rule them by the Book of Allah (SWT) and the Sunnah of the Messenger (SAW). The responsibility of the Khaleefah is to implement the Islamic shari'ah and carry the Islam daw'ah to the world. The KHILAFAH ruling system is unique and distinguished from all the ruling systems in the world. It is not a theocratic state; rather it is a state based upon an ideology which is obligated to provide security and ensure the basic needs for all of its citizens regardless of race or religion.
Throughout its existence the KHILAFAH state was the flower of the globe, the rising sun amongst nations and beacon of hope for oppressed peoples of the world. Mankind progressed under its leadership and found peace, security and true prosperity under its shade. It is an undisputed historical fact that for more than 1300 years the KHILAFAH state led the world politically, militarily economically, spiritually and intellectually. No nation on earth could compete with the Islamic Ummah as long as she was under the leadership of the KHILAFAH.
The KHILAFAH state existed in the world from the time of Muhammad (SAW) until its abolition on 28th Rajab 1342 AH (3rd March 1924 CE) at the hands of colonialist Britain and her agent Mustafah Kamal, may Allah (swt) curse him. As a result of the abolition of the KHILAFAH, the Muslims today are divided over 50 states and have lost the shield to protect their lives, honour and property. The Messenger of Allah (SAW) said,
الإمام جُنَة يقاتل من ورائه ويتقى به
"The Imam is the shield behind whom you fight and protect yourselves." (Muslim)With the abolition of the KHILAFAH, we have lost our caretaker who will take care of our affairs and solve our problems. We are now living under kufr states who implement kufr ideologies over us. Moreover the disbelieving imperialist powers have imposed their agents to rule over us such as Musharraf, Karimov, Bashar, Mubarak, Karzai, Abbas and Fakhruddin. Our enemies perceive us to be weak and leaderless and launch attacks upon us like predators. Palestine, Kashmir, Bosnia, Kosovo, Chechnya, Afghanistan, and Iraq – the list is endless. Today all guns are targeted at a Muslim. The Muslims today are divided and weak to the point that when America and her allies are launching their aggression upon one Muslim country after another in the name of 'the war against terror', there does not exist one single ruler in the Muslim world to bravely stand up for Islam and the Muslims. At the same time the capitalist ideology with its slogans of freedom and democracy, which is implemented upon the Muslims toady, has failed to bring any good for the Ummah. In fact this colonial ideology has brought the entire humanity to the verge of destruction.
O Muslims!
The KHILAFAH state is the most important obligation from your Lord. It is the source of your glory; it will defeat your enemy and liberate your lands. It will be the beacon of goodness and justice throughout the world. On the occasion of the destruction of the KHILAFAH,
Hizb ut-Tahrir in Bangladesh calls upon you to engage in the work for re-establishing the KHILAFAH with utmost effort and speed so as to abolish the rule by kufr and resume the rule by what Allah (SWT) has revealed. As long as we continue to live by the man made kufr systems and neglect our duty to establish the Islamic ruling, we will be accumulating the sin on our necks. After embracing the aqeed'ah of Islam, working for establishing the rule by what Allah (SWT) has revealed is one of the most important obligations upon the neck of a Muslim. Furthermore fulfilling this obligation is not the responsibility of any specific party or group only; rather it is a fardh from Allah (SWT) upon the entire Ummah. Allah (SWT) says,
فَاحْكُم بَيْنَهُم بِمَا أَنزَلَ اللّهُ وَلاَ تَتَّبِعْ أَهْوَاءهُمْ عَمَّا جَاءكَ مِنَ الْحَقِّ ..." المائدة48.."
'So judge among them by what Allah has revealed, and follow not their vain desires, diverging away from the Truth that has come to you.'(Surah Al-Ma'idah:48)
كانت بنو إسرائيل تسوسهم الأنبياء، كلما هلك نبي خلفه نبي، وإنه لا نبي بعدي، وستكون خلفاء فتكثر، قالوا فما تأمرنا؟قال:فُوا، ببيعة الأول فالأول، وأعطوهم حقهم، فإن الله سائلهم عما استرعاهم
Muslim reported on the authority of Abu Hazim, who said: "I accompanied Abu Hurayrah for five years and heard him talking of the saying of the Prophet (SAW): The Prophets ruled over the children of Israel, whenever one Prophet died another succeeded him, but there will be no Prophet after me. There will be Khulafaa' and they will number many. They asked: What then do you order us? He (SAW) said: Fulfill the bay'ah to them one after the other and give them their due. Verily Allah will ask them about what He entrusted them with." 
