Fall of Nineveh
For better or worse, the United States of America is starting to withdraw as the arbiter of global peace. This role is falling to powers that operate at a more regional level, with more regional concerns. One of these areas is the Middle East - a part of the world that has seen a significant amount of American investment in bullets, blood and greenbacks. As the United States tries to wrest its feet from the sandy morass that it dove into in response to the attacks of 9/11, local players are filling this vacuum with their own interests; these interests are extremely unlikely to coincide with American interests.
There are three powers to keep an eye on in this theater - the first is Turkey. Once aligned strongly with American interests in hopes of joining the European Union, Turkey has recently taken a hard slant toward despotism and seems to be preparing for an upcoming ethnic conflict with Kurds after the Islamic State is suppressed. This conflict will embroil Turkey terribly and might cause it to be kicked out of NATO - such action could also reignite the frozen conflict in Cyprus with Greece. Nationalists and crusaders in the West salivate and fetishize the reconquering of Constantinople from the forces of Islam - such action is fantasy that only serves as propaganda. If external conflict comes to Turkey, it will come in the form of Turkey's banishment from NATO followed by Russian interference in the Caucasus trying to benefit Armenia against Azerbaijan. Armenia has an antagonistic attitude toward Turkey because of the (denied) genocide during World War One, and Russia has long-held ambitions in the Black Sea, one of which is the reconquest of Constantinople for the forces of the Orthodox Patriarch. Perhaps this makes the worship of Putin by non-Russian nationalists easier to understand.
The second is Iran. An ethnically and politically diverse nation currently controlled by religious fanatics, Iran has shown outward signs of liberalization and commercialization. But the going has been slow, and Iran still has the reputation of being an exporter of terror. Such reputation is not baseless - terror attacks were very much an official doctrine of Iran from the 1980's into the 2000's, but Iran has now taken a different role. Once consigned into being the purse for Hezbollah in their fight against Israel, Iran's military affairs have greatly expanded. Not only providing material and logistical support for al-Assad's forces in Syria, Iran has also deepened its influence in Iraq. Instead of clandestinely supporting al-Sadr's militia, Iran is openly intervening in Iraq against the Islamic State. Iran is also supporting the Houthi resistance against the Saudi-backed government in Yemen, the latest front in the ideological war between Shia and Sunni of which Iran is the champion of the Shia.
The champion of the Sunni is the third power - Saudi Arabia. The Saudi family rebelled against the Hashemite family that was installed by the British Empire to rule the Arabian peninsula and consolidated their power among the religious custodians of Mecca and Medina and the fiercely traditional tribes of the Arabian interior with adherence to Wahhabism - a theologically regressive Sunni ideology that attempts to make its adherence live their lives exactly as Muhammad and his followers did in seven-century Arabia. All religions have different sects, and all messianic religions have those sects that see deviance from the lifestyle of the messiah as sin and try to bring the sheep back to the flock - some with celebrations of ecstasy at oneness with god as the Sufis do, others with a firm adherence to law and order, as the Wahhabis do. As oil money poured into the kingdom, madrassa funding poured out all across the world, spreading the Wahhabi sect to become one of the loudest, fastest growing and most influential Islamic sects in the world, with dire results.
For such firm adherence to law and order that the Wahhabi's demanded can be much harsher against other Muslims than against explicit non-believers. This is analogous to how traitors are perceived in relation to foreigners - those that betray are generally seen in a more negative light then those that are explicit in being apart from the flock. This attitude is the reason why Muslims are the most frequent target and largest sufferers of terrorist attacks, and partly why Iran and Saudi Arabia are in a death struggle. Each champions a wing of the ummah (the Muslim community) that sees the other as an intrinsic threat to the integrity of the ummah. The blood shed over this disagreement spans centuries and never truly stopped - but imperialism did pump the brakes a bit. The dominion of the Ottomans, the Safavids, the British and the French made such open religious civil wars out of the question. But in lieu of the hegemony and forced peace (if such a situation could ever be called peace) of direct American influence, these disagreement can become increasingly loud.
The American invasion of Iraq and subsequent civil war there was but a prelude to what is likely to come - Saudi Arabia and Iran have been preparing for this head-to-head since 1980. The war between Iran and Iraq was not just a feud between religions - Iran was recently taken over by fundamentalist clerics who needed to suppress dissident liberals, communists, monarchists and moderates. The invasion of Iran by Iraq gave Ruhollah Khomeini what he needed as Ayatollah of Iran - a common enemy. Saddam Hussein had recently come to power in Iraq, and desired a strong cult of personality to echo his idol, Joseph Stalin. Seeing military victory as a great way to boost his standing both among his people and across the Arab world, Hussein attempted to seize Arab-majority oil-rich Khuzestan province in southwestern Iran by escalating a dispute over maritime traffic in a river.
The ensuing war saw both sides utilizing their cultural heritage to rally its people - Iraq calling back to Babylon and Assyrian Nineveh, Iran summoning the memory of Persia. They also used religion as a tool - Iran was almost completely Shia; Iraq was a conglomeration of majority Shia, Arab Sunni, Kurd Sunni, Yazidi, and Syriac Christians ruled by a secular, practical and paranoid dictator. The Ayatollah used Iran's religion as a shield against heretical Sunni, capitalist American and communist Soviet attempts to subjugate Iran, while Hussein used his religious ambiguity as a rally against religious fanatics while also courting arms and logistics from Americans and Soviets. Capriciously, America and the Soviet Union would intermittently support Iran as the conflict swung back and forth. Turkey, for its part, profited enormously from this war by being the black market for Iran. Saudi Arabia was in a less envious position.
Saudi Arabia was not only doctrinal rivals to Iran on a religious basis, they were terrified by the possibility of Iran becoming a regional hegemony. If Iran would win the war (and after the initial Iraqi invasion, Iran almost constantly had the initiative), it could forcibly seize all the Shia-populated lands in Iraq. This included most of southern Iraq (which bordered Saudi Arabia) and included several enormous oilfields. Iranian control of these oil fields would give them enormous revenue and fund their ongoing ascendancy - after all, if the Ayatollah was able to secure his power in Iran by military victory, he would naturally believe he could maintain it the same way. Considering the Ayatollah declared the overthrow of the Saudi regime a war goal, it is no surprise Saudi Arabia began financially subsidizing Iraq once their offensive stalled.
The Iran-Iraq war would end up being a bloody stalemate that only served to exacerbate long-standing ethnic and religious animosity while consolidating the control of religious fanatics in Iran and a totalitarian sociopath in Iraq. The sociopath has been dead a decade, but in his void a vacuum in Iraq exists that has yet to be filled. The Kurds in Iraq will demand self-rule, and the Kurds in Syria and Turkey will likely wish to join them. Turkey will bully anything approaching Kurdish independence. Iran will continue to entrench among allies old in new in Iraq and Syria. Saudi Arabia will try to balance having lower revenue from lower oil prices with having to counter Iranian attempts at hegemony while embroiled in a costly civil war in Yemen.
The United States is overtly supporting Saudi Arabia while opposing Iran and in a confused relationship with Turkey. I hypothesize that if open war does break out, Saudi Arabia and Iran will be the primary belligerents, most likely involving trade in the Persian Gulf. Erdoğan will take a page from the book of strongmen and use war to centralize his power. In the wake of the Kurdistani self-rule that will likely be enabled in Iraq, protests in Turkish Kurdistan will increase. Explosions will occur at a variety of densely-packed populated centers, which will be attributed to Kurdistani terrorists. Turkish soldiers will enter Iraqi Kurdistan using the casus belli of suppressing terrorist support, which is essentially the same pretense America used to invade Cambodia in the Vietnam War. This will all be happening around and inside Iraq - a country that has been in some form of religious civil war for over a decade. One could argue that Iraq can stay steady, united and strong in the face of all of this, but it is a tough argument to make.
Escalation from there is almost inevitable. It is hard imagining Russia not trying to guide events in its own interest, and its involvement in the Syrian civil war and relationship with Iranian expeditionary forces give hint to what may come. The guiding that America will do is less decisive and increasingly more questionable.