The term Islamic empire can refer to any one of several Islamic republics in existence in the modern era, but is more often a reference to the realms ruled by claimants to the succession to the Prophet Muhammad. Additionally, the term can refer to the first Islamic empire that emerged from the Muslim conquests of the Middle East, parts of Asia and North Africa following the rise of the religion in the Arabian Peninsula. The early Islamic Empire, or its seat of rule, was called the Caliphate, roughly translated as the "replacement" or the "steward." Its early leaders were elected in a sort of electoral monarchy in the style of tribal elections in the Arab peninsula.
Following a long war between Muhammad in Medina and his opponents in Mecca, Muhammad led the people of Medina and by defaults his followers to conquer the city of Mecca after an eight year war with Mecca. Shortly afterward, Muhammad passed away, leaving the dominions the Muslims had conquered fractured and the religion struggling to hold on. Abu Bakr, Muhammad's elected successor, launched the Apostate wars which were considered political, but have religious meaning for Muslims. Abu Bakr's efforts eventually conquered the Arabian Peninsula for the Muslims. Perhaps owing to their need not to launch wars against fellow Muslims, Arabian raiders set their sights on the Sassanid and Byzantine empires. By 637, the Caliph Umar had conquered the bulk of what is now Syria and Iraq, plus severely weakened the crumbling Sassanid Empire of Persia. By 642, the Persian army was totally defeated at the Battle of Nahavand, ending the Persian Empire. In 639, the Muslims invaded Egypt under the leadership of Amr ibn al-Aas.
The Umayyad Dynasty held sway until the middle of the 8th century, by which time the Muslims had crossed into Transoxiana, explored India and conquered Spain. The speed at which the Muslims conquered these territories is considered the swiftest change in political alignment in human history. Spain was ruled by the Umayyad dynasty until 1031.
As time went on, the Arab dynasties imported Turkic slaves from central Asia to be trained as elite soldiers, commanders and administrators. The growth in the number of these people eventually created a Turkic upper class that seized control over the areas in which they worked. After the decline of the Ayyubids in Egypt, the Mamluk Sultanate, composed of such Turkic-descended elites, consolidated control of the country and went on to conquer the Upper Nile and Levant, becoming both the most powerful Muslim empire of the time and the most formidable foe to the encroaching Mongols. There was Mongol settlement in the Middle East, in modern Iran, which became part of the Ilkhanid Empire in which many Mongols converted to Islam. A number of Muslim polities were founded as time passed, reaching as far as India, which commonly ruled over majorities of subject Christians or Hindus.
By 1517, the emergent Ottoman Empire had conquered much of southeastern Europe and Anatolia, and finally toppled and conquered the Mamluks. The Ottomans claimed the Caliphate for themselves and became the most formidable empire at the same time that the Europeans began to extend their naval power. The Ottoman conquest of Egypt ushered in a period of Islamic practice in the realm. As the Ottomans stopped their conquests into Europe, the empire began a gradual decline that was alarming enough to provoke the Ottoman elitists to lobby for major reforms mirroring European governing practices. A number of European states sought alliances and disproportionately favorable agreements with the Ottoman leadership. Eventually, secular policies came to dominate the empire through a series of reforms, and Islam was less dominant as a new secular elite rose to prominence. After the dismantling of the empire following WWI, Turkey emerged as a nation state. The Caliphate was dissolved, leaving bitter feelings with pious Muslims and fueling the beginnings of Islamic fundamentalist movements closely integrated with anti-imperialist ideology. Today, certain religious movements but no one country claim the Caliphate. Some countries opt to call themselves Islamic republics, including Iran, Afghanistan and Pakistan.