Map 1 shows the Khuzestan Province of Iran, map 2 shows the Eastern Province of Saudi Arabia, and map 3 shows the reserves of oil (black) and natural gas (red) of the region. Arab Shiites (Shia) are the majority in both Khuzestan (Iran) and the orange area of the Eastern Province (Saudi Arabia). As you can see from map 3 both regions are very rich in oil and natural gas reserves. The problem for Iran and Saudi Arabia is that the Iranians are Persian Shittes and not Arab Shiites, and the Saudis are Arab Sunnis and not Arab Shiites.
Map 1 Khuzestan Province
Map 2 Eastern Province of Saudi Arabia
Map 3 Reserves of Oil (black) and Natural Gas (red)
The Iraqis, mainly during Saddam Hussein’s rule, wanted to annex parts of Khuzestan by using the Arab Shiites of Khuzestan, and the Iranians, especially today, want to destabilize the Shiite parts of the Eastern Province of Saudi Arabia by using the Arab Shiites of Saudi Arabia. The Iraqis have the advantage over the Iranians that their agents in Khuzestan can promise everything to everybody, and the Iranians have the advantage over the Saudis that their agents in Eastern Province can similarly promise everything to everybody. When I say they can “promise” I mean in terms of social spending and increased freedom.
When the Iranian Islamists rose to power in 1979, and they nationalized the Western oil companies, thus destroying their alliance with the West, Saddam Hussein, who was a Soviet ally, grabbed the chance and invaded Iran, knowing that the West would not help the Iranians. Moreover Saddam Hussein knew that the Iranians scared the Arabs of the Persian Gulf more than him, and therefore the Arabs of the Gulf would have to support Iraq, because they would not want to see the Iranians bringing to power the Shiite majority of Iraq.
Note that Arab Shiites are the majority in Iraq, and Saddam Hussein ruled Iraq with the Sunni minority of the country. Exactly the opposite was going on in Syria, where the Alawite minority, which is an offshoot of Shia Islam, was governing the Sunni majority. Anyway, among other things Saddam claimed some parts of the rich in oil Khuzestan when he invaded Iran.
However Saddam Hussein failed to annex any Iranian regions during the Iraq-Iran War 1980-1988. Iran was mainly supported by China, North Korea, Syria and Libya. However the West, the Soviets and the Chinese did not get as much involved as the Arabs did. It was mainly the French who were selling arms to Saddam Hussein, and it was mainly the Arabs of the Persian Gulf who were paying for these arms. For the uprising of the Arab Shiites of Khuzestan after the Islamist Revolution of 1979, and also the Kurdish uprising of Western Iran during the same time, see Wikipedia “1979 Khuzestan uprising”.
Today we witness almost the same story happening in the Eastern Province of Saudi Arabia. Saudi Arabia has seriously hurt her alliance with the United States, and the Saudis have lost the American protection they enjoyed in the past. The Iranians, feeling the Saudi weakness, they are supporting a revolt in the Shiite regions of Saudi Arabia. The Shiite cleric that was executed by the Saudis on January 2016, causing a deepening crisis in the Iranian-Saudi relations, was an enthusiastic supporter of the Shiite uprisings in 2011, when the Arab Spring broke out in Saudi Arabia. For the Shiite uprising in Saudi Arabia see Wikipedia “2011–12 Saudi Arabian protests”.
It is very interesting that the Sunni Arabs of Saddam Hussein and the Shiite Persians of Iran today are both using Arab Shiites. Saddam was using them in order to attack Iran in the 80s, and the Iranians are using them to attack Saudi Arabia in the 21st century. Today, the official government of Iraq, which is controlled by Arab Shiites, has aligned herself with the Iranians, hoping that together they will manage to reach the Mediterranean Sea through Syria. Syria is a strong Iranian ally. That does not mean of course that the Arab Shiites of Iraq cannot change sides in the future, and align themselves with the Turks and the Sunnis, if they feel it is easier to send their oil and gas to Europe through Turkey.