It is a great irony that Quran speaks about unity and rejects the division of religion in sections among Muslims however fact is that Muslim community has many divisions and sub-divisions like Shia and Sunni which evolved after the demise of Prophet Muhammad.
Quran gives the message of brotherhood & asks to refrain from sects in Surah 3. Al-i'Imran, Ayah 103:
“And hold firmly to the rope of Allah all together and do not become divided. And remember the Allah has bestowed blessings upon you - when you were enemies and He brought your hearts together and you became, by His favor, brothers. And you were on the edge of a pit of the Fire, and He saved you from it. Thus does Allah make clear to you His verses that you may be guided. He explained to everyone the meaning of love and also told them how all were different and how all became brothers. ”
It guides not to make distinct groups in Surah 6. Al-An'am, Ayah 159:
“As for those who divide their religion and break up into sects, - thou hast nothing to do with them: their case rests with Allah alone; He will in the end tell them the truth of all that they did.”
Muhammad was the founder of Islam. He was Engage in Jiyad for the sake of Allah & serve Humanity. But someone misunderstood the meaning of jihad. Muhammad did not name any successor before his death in 632 AD and this resulted in the first ancient origin of sects among Muslims, First four Caliphs began the Sunni tradition, however, Caliphs rule could not last after the fall of Ottoman empire (Modern Turkish).
Shias consider Ali as the divinely appointed successor of Prophet Muhammad consider him Caliph who was from the direct lineage of Muhammad and was his son in law whereas Sunnis consider previous three (Abu Bakr, Umar, and Uthman) also. Having followed different successors resulted in the evolution of different classes afterward.
Shia Muslims emphasize the special spiritual and political leadership of imams (Muslim religious leaders) to Muslim society. Unlike Sunni who prays five times, Shia Muslims pray three times during the day. Shia and the Sunni also differ in some interpretations of the Qur'an and Hadith and even each has a different canon of Hadith as well as they differ in five pillars of Islam which are fundamental aspects of Islam.
A detailed study of more than 200 countries finds that there are total 1.6 billion Muslim adherents all over the world as on today & 80% of world Muslims live in countries where Muslims are in majority.
Among these, 10-13% are Shia Muslims and remaining majority are Sunni Muslims. Indonesia, Pakistan, and India inhabit maximum which amounts to 33% of total world Muslim Population of all ages. Between 70 to 80% Shia population lives in countries India, Iran, Pakistan, and Iraq.
Entered Eastern and Southeastern Europe shortly after its inception in the 7th century and later the 13th Century and has established themselves in almost every country of Europe now. In 20th Century and early 21st Century, the large number of non-native Muslims have immigrated to Europe which constituted 6% by 2010.
Germany and France have largest Muslim population among all countries of European Union and most of these Muslims and from Sunni class.
According to a study, more than million Muslims have immigrated to Europe since the outset of Syrian Crises & authorities are worried about the insurgence of terrorist in the form of refugees who can commence military jihad against them.