Iran and Iraq are bastions of Shi'a Islam for several different reasons.
1) Birthplace of Shi'a: Southern Iraq was where 'Ali, Hussein, and Hassan, the important figures who formed the basis for Shi'a Islam, lived and (in the case of Hussein and Hassan) were murdered by Mu'awiya's servants. The cities of Karbala and An-Najaf in Southern Iraq are part of this story.
2) Persian Cultural Center Discrimination: Persia was always a high seat of culture in the Islamic Empire. As a result, ideas moved quite freely throughout Persia and Persians considered themselves to be of equal worth to Arabs. Under the Sunni Umayyads, Mawali (non-Arab Muslims) were second class citizens. Since Shi'a were also discriminated against, the Persians and the Shi'a began to unite to help overthrow the Umayyads by supporting the Abbassids. This relationship resulted in some Persian converts to Shi'a Islam.
3) Safavid Dynasty: The Safavids of Iran (of the 1500-1700s) were Shiite Religious Zealots and converted masses of Iranians to Shiite Islam.
4) Holy Sites: Because of the tumultuous birth of Shi'a Islam in Iraq, there are a number of Shiite Holy Sites in Iraq and those naturally attract Shi'a populations.
Traditional Answer
After Karbala tragedy most of Iranians and Iraqi Sunni Muslims converted to Shi'a.
Historical Answer
Iran did not become majority Shi'a until the 1400s and 1500s under the Safavid Dynasty which invested heavily in proselytizing Sunnis to become Shi'a. Iraq had maintained a large Shi'a population on account of the Karbala incident, but the majority of families that converted to Shi'a did so around the same time as those in Iran. However, Iran and Iraq have almost always been the most concentrated regions of Shi'a Islam even though numerous other dynasties such as the Fatimids in Egypt and the Idrissids in Morocco were also Shi'a.
Most Arabians practice Sunni Islam, but there are significant minorities of Ibadi Muslims (in Oman -- where they are the majority) and Zaydi Shiite Muslims (in Yemen). Most of the Arabs in Saudi Arabia identify strongly with the Wahhabist Strain of Sunni Islam.
All groups of Syrians are currently fleeing Syria, from the majority Sunni Arab Muslims, to numerous ethnoreligious minorities, like Ismailis, Kurds, Assyrians, Shiite Arabs, Druze, and Alawites.
the issue that divied them was they developed differences
they are two sect or fraction of Islam religion. Sunnism as Majority and Shiite as minority are two main sects in Islam religion.
The largest Shiite communities are in Iran, Azerbaijan, southern Iraq, Bahrain, and northern Yemen. The Sunni communities are spread throughout the Middle East, North Africa, Southeast Europe, South Asia, and Indonesia. There are, of course, minorities of Sunni and Shiite Muslims throughout the world.
No. They are almost all Sunni Muslims.
There are more Sunni Muslims than Shiite Muslims. Shiite Muslims represent about 15% of the global Islamic community whereas Sunni Muslims represent 85%. The numbers of the other sects are negligible.
In Iran. Refer to related question below.
Certainly Iran. Iraq and Azerbaijan are also majority Shiite countries. Other countries like Lebanon and Yemen have large Shiite minorities.
Sunni and Shiite, with Sunnis being the majority of 85% of all Muslims.
Iran is an Islamic country with the wide majority of it population are Shiite Muslims.
Yes, he is shia. majority of Iraq people are shia Muslims.
YES. There were a number of Islamic countries that were sectarian in their outlook and, therefore, expelled Muslims who were believed to be of the wrong sect. The most clear attempts at this in the pre-modern era were the persecution by the Ottomans of the Shiite and Alevi minorities and the persecution of the Sunni minorities in Safavid Persia. In more recent times, the persecution of the Ahmadiyya minority in Pakistan, the forced relocation of Sunni and Shiite Iraqis, and the low-level ethnic cleansing of Hazaras in Afghanistan are examples of Muslims being expelled on account of their sect in Muslim-majority countries.
Yes. But they were not Twelver Shiites; they were Shiite Muslims of the Ismaili (Sevener) School.
As far as I am aware, there is no Shiite Islamic community in Israel. The Muslims in Israel are primarily Sunnis.
A Persian is a native or inhabitant of Iran. The majority of Irani are Persian Shiite Muslims. It is possible that they originally migrated from Asia or central Europe.
Oman is actually majority-IBADI, which is a minority sect in Islam that represents less than 1% of all Muslims.