Why do the Sunnis and Shiites not get along?

Answer 1

They get along but Slafi Muslims (like ISIS, Al-Qaede, Wahhabis,...) do not get along with both Shia and Sunni Muslims. they want to make war between Shia and Sunni and media Propaganda shows that it is Shia/Sunni war. for example in Iran Shia and Sunni are living in peace and pray at common mosques. but ISIS is a different matter. it is managed by Israel to "Divide and Rule" Muslims.

Answer 2

First of all, most Sunnis and Shiites get along just fine. It is a vocal and violent minority, especially political leaders and terrorist organizations that are responsible for discrimination and violence. Even then, it depends entirely on which Shiites and which Sunnis are fighting and more often than not it does not require outside interference.

Sunni Repression of Shiites
Many of the historic Sunni Muslim Empires actively repressed and persecuted Shiite Muslims. The seminal event beginning this persecution was when Yazid I of the Umayyad Caliphate ordered the execution of Imam Hussein and a large remnant of the Ahl al-Bayt (Prophet Mohammed's family). At this point in time, the Shiites were a political faction supporting Ahl al-Bayt over the Umayyad Caliphs. The murder of Hussein began to transform the identity of the Shiites and plays a central role in their beliefs. The Umayyad Army followed through with this. Additionally the Umayyad government wanted to create a Sunni Arab aristocracy and therefore applied the jiyza tax not only to Jews and Christians, but to Mawali (non-Arab Muslims) and the Shiite Muslims, regardless of whether they were Arab or Mawali. Shiite Muslims were also banned from most government positions under the Umayyads. Finally, the Umayyads continued to seek out the Shiite Infallible Imams, torture them and murder them.

Shiite Muslims joined arms with the Sunni Abbassids in 750 CE who promised a better situation for the Shiite Muslims, but they were later deceived. The Abbassid Caliphs continued the Umayyad trend of torturing and murdering the Shiite Infallible Imams, but extended this as well to Shiite leadership (Mullahs and Faqihs). Shiite Mosques were destroyed and worshipers during Ashura processions were murdered. Shiite Muslims and their property were also periodically attacked as scapegoats for Abbassid military problems, such as the Byzantine offensive in 971 CE. The Abbassid Caliphs also provided financial support to those Faqihs (Islamic Jurists), especially from the Hanbali School, that would propagate anti-Shiite attitudes.

The Ottoman Empire saw the Shiites under its purview incorrectly as a fifth column for its rival in Persia, the Safavid Empire, which was a Shiite Islamic State. To prevent Shiite Muslims from becoming a critical mass in the country, the Ottomans massacred large numbers of Shiites, especially the Turkish Alevis, the Syrian Alawites, and many Lebanese Shiite Muslims (mostly Twelvers).

Currently, there is government-level repression of Shiite Islam in several countries, including Bahrain and Saudi Arabia. In both of these countries, the Shiite population (66% and 15% respectively) are actively banned from government positions, have many sectors of the economy closed to them, and have minimal say even in their own protection. In Saudi Arabia, Wahhabis have issued fatwas against Shiite Muslims, written textbooks slandering their faith, actively banned Ashura and other Shiite festivals, and in some cases prevented the creation of Shiite burial grounds. In other countries, such as Indonesia and Pakistan, violent Radical Sunni-Affiliated Groups terrorize portions of the Shiite population and the government takes no action to protect the Shiite Muslims. Finally, there are a number of Muslim countries like Malaysia, where Shiite Muslims are on good-footing with Sunni Muslims but are prohibited from open proselytization.

Shiite Repression of Sunnis
However, the Shiites have also persecuted Sunnis under their watch. The first major attack of Shiites against Sunni leadership was in the final days of the Fatimid Caliphate when Fatimid rulers created the Assassins who took down many notable Sunni leaders such as Grand Vizier Nizam ul-Mulk of Baghdad, Mohammed Ghori, the Atabegs Maudud and Zengi of Mosul. The Assassins even targeted Saladin the Ayyubite, but were unsuccessful.

The Persian Safavids fought several wars against neighboring Sunnis in Samarqand to the North and the Ottomans to the West. Ismail I (the first Safavid) adopted Twelver Shiite Islam and began to persecute the Sunnis in Iran. This reduced their community to a small minority in the Persian heartland. He destroyed numerous Sunni mosques and grave sites as well as mandating curses against the first three Rightly-Guided Caliphs. He also imprisoned and killed large populations of Sunnis for their beliefs and compelled conversion to Shiite Islam through violence. The Safavids also spread this form of Sunni oppression through conquest Azerbaijan and of southern Iraq and imposing conversion to Shiite Islam there as well.

There are also current examples of repression of Sunnis by Shiites. Since the Islamic Revolution in 1979, Shiite repression of Sunnis has become dominant again in Iran. Sunni Iranian Cleric Abu Muntasir Al-Baloushi has said that the government of Iran (because of its repressive practices towards Sunnis) is a greater threat to Islam than even Israel. In Iraq, Shiites and Sunni militants fight for the attempt to have greater control of the government after America removed Saddam and each group sought to advocate its views to the suppression of the other. As the Shiites are more numerous in Iraq, they seem to have the upper hand in determining policy. In Syria,the current civil war is between a secular Shiite-led government and the majority Sunni population of Syria which has historically been denied the same accessibility to jobs, healthcare, and living-standards.