Relations between the Kingdom of Saudi Arabia and the Islamic Republic of Iran have never been particularly good.  But with the execution of Shia cleric Sheikh Nimr al-Nimr on January 2, relations are deteriorating further and faster.

The next day, Sunni Saudi Arabia and Shia Iran severed ties with one another, and each gave the other's diplomatic staff 48 hours to leave the country.  That was in reaction to Iranian demonstrators storming the Saudi embassy in Tehran.  

The BBC reported last Monday that Saudi allies Bahrain and Sudan are also severing diplomatic ties with Iran, giving the Iranian diplomatic staff 48 hours to vacate the respective countries.  The United Arab Emirates, another Saudi ally, has downgraded its diplomatic representation in the Islamic Republic. 

But the current turmoil is only a small aspect of a greater struggle that is as old as Islam itself.  Probably the most important aspect of the schism between the Sunnis and Shiites (Shia) was the succession after the death of the prophet Mohammed.  The Sunnis believed that Mohammed's confidant Abu Bakr should succeed him, while the Shiites have insisted that Ali ibn Abi Taib, Mohammed's son-in-law and cousin, should be the new leader of Islam.

In A.D. 661, Ali was killed by a Sunni faction while at prayer in the Great Mosque of Kufa.  Ali's murder cemented the division between the Sunnis and Shiites.

The defeat of the Ottoman Empire in the First World War would essentially create the endless chaos we see today.  In that context, the single most consequential event with regards to Middle East politics is the Sykes-Picot Pact.  The secret agreement between England and France partitioned much of the former Ottoman Empire into direct-rule regions and spheres of influence.  The two Great Powers attempted to partition the land among tribal and religious lines.  However, according to Tarek Osman of BBC News, "the thinking behind Sykes-Picot did not translate into practice. That meant the newly created borders did not correspond to the actual sectarian, tribal, or ethnic distinctions on the ground."

The Pew Research Center conducted a poll in 2012 that showed that among most of the Sunni Muslims of the Middle East and North Africa, at least forty percent do not accept Shiites as fellow Muslims.

The Middle East and North Africa are, for the most part, divided into Sunni- and Shia-majority countries.  Saudi Arabia, the United Arab Emirates, Kuwait, Jordan, and Qatar, as well as Pakistan, Somalia, and Indonesia, are Sunni-majority countries.  Bahrain, a Shia-majority country, is ruled by a Sunni monarchy allied to the Saudis.  The government in Bahrain witnessed a major uprising in 2011 during the Arab Spring, and Bahrain accused Iran of supporting the uprising.  Iran and Iraq are Shia-majority countries.  Although Iraq is technically a Shia-majority country, it is close to being evenly split (51% Shia, 42% Sunni).  Iraq, under Saddam Hussein (a Sunni), acted as a counterweight to Shia Iran.  Iraq's government is now under Shia control.  Syria is a Sunni-majority country ruled by an Alawite (Shia sect) minority. Muslims in Yemen and Lebanon are evenly split among Sunnis and Shiites.

Since the 1979 Iranian Revolution, the regime in Tehran has openly criticized the religious legitimacy of the monarchy in Saudi Arabia.  During the Iran-Iraq War (1980-1988), Sunni Saudi Arabia backed Sunni Iraq under Saddam Hussein against Shia Iran, which was backed by Syria.

In 1987, during the annual Hajj pilgrimage to the holy city of Mecca, Iranian pilgrims began demonstrating against the United States, Israel, and the Saudi government.  The demonstration soon turned violent, and Saudi police moved in.  After the chaos was over, more than 400 people were dead (including 275 Iranian pilgrims and 85 Saudi police), and nearly 650 people were wounded.  In reaction, the Iranian regime called on the Saudi people to overthrow the Saudi monarchy.  The Saudis replied by banning all Iranians from entering the country to take part in the Hajj.

Mecca would see another, even worse, incident.  During the Hajj in September 2015, a bottleneck formed at an intersection involving several crowds.  In the ensuing turmoil, the Associated Press estimated that nearly 2,411 people had died, with thousands more injured.  The Saudi government's official casualty numbers were 769 dead and 934 injured, which were considered by most governments to be underestimates.  The Iranians lost 464 (the most of any country) of its citizens and led worldwide outrage toward the Saudi government.

Relations between the two countries became increasingly strained after U.S. officials uncovered an Iranian-tied plot to kill Adel al-Jubeir, the Saudi ambassador to the United States, at a restaurant in Washington, D.C.

Saudi Arabia and Iran are currently engaged in two proxy wars, in Syria and Yemen.  The Iranians are backing the Syrian government under Bashar al-Assad, while the Saudis back the Islamic Front, part of the Syrian opposition.  The Islamic Front is not recognized by the internationally recognized Syrian National Coalition.  The Islamic Front is conglomerate of different groups numbering about 60,000 fighters looking to install in Syria a Sunni/Salafist government based on sharia law.

In Yemen, the Saudi government has poured 100,000 troops into the country and has carried out numerous airstrikes to support the internationally recognized government of President Abd Rabbuh Mansur Hadi.  Iran, on the other hand, has been supporting the Houthi militants who fight for the Revolutionary Committee that had overthrown President Hadi.

Although Saudi Arabia is not openly hostile toward the nuclear deal with Iran, the Saudi government has expressed concern with the United States trusting its long-term adversary.  Additionally, relations between the Saudis and the United States have been strained lately.  The Saudis are worried that the United States is not fully committed to bringing order back to Syria and stabilizing Iraq, and they also worry that Iran might not honor the nuclear agreement, which would lead to a nuclear arms race in the most volatile region in the world.

Politically, the recent crisis between Saudi Arabia and Iran will only add to the notion that President Obama is weak and feckless.  The entire world seems in disorder and taking on water, and no one is at the helm.  The United States, under Obama, is not in a position to defuse the situation.  Iran, after getting what it wanted from the nuclear deal, has no reason to listen to our president about a decades old feud with Saudi Arabia.  Saudi Arabia doesn't believe that the United States will have its best interests at heart, given the détente between the U.S. and Iran.

The next president, Republican or Democrat, will have a full plate – make that a buffet – of problems to face, and to face quickly.  The Democrats don't have any solutions, so the Republicans should be talking more about how they can bring order back to the world.