Why didn't the Ottomans conquer Persia?

The Ottoman Empire secured its place as one of the most powerful and large empires throughout its 600 years of history. It was the empire that seized Constantinople and collapsed the Byzantine Empire, and its cultural expansion still remains throughout some of its former vassal states today. But there will always be curiosity as to why any empire stopped where it did, and what prevented further growth before the ultimate collapse. In the case of the Ottomans, one question that comes to mind is why didn't the Ottomans conquer Persia? There are a few major factors that contributed to why Persia, now Iran, never became a part of the Ottoman Empire. Firstly, the topography of the region between modern-day Turkey and Iran posed an irreversible challenge. Despite the two nations sharing a border, the land between the empires was full of mountain ranges and desolate valleys. Access to fresh water was minimal, and the journey from Constantinople and into Persia, a particularly large territory as well, would have utterly exhausted the Ottoman troops. Even if they could have supplied themselves well enough to successfully make the trek, by the time they arrived at their destination, they would have been fatigued. Any harassment or guerrilla tactics from the Persians would have put an overwhelming amount of pressure on the Ottomans. In the case that somehow the latter was able to reach their goal destination unseen, they would have needed significant rest before battle, and after the fact, would still have to march all the way back home. Such a rough journey would have then made it easy for the Persians to retake any lost territory as the depleted Ottoman forces made their way back to Constantinople. It simply would have been nearly impossible to have any success with such difficult terrain and distance to overcome. Nonetheless, the Ottomans and Persians were staunch adversaries due to religious disputes. The Ottomans were semi-Muslims, while the Persians, particularly the once-magnificent Sefafids, were Shiite Muslims. This meant that, regardless of the odds being stacked against the Ottomans, they actually did try to take on the Persians not once, but multiple times, in a series of Ottoman-Persian wars beginning in the 16th century. So let's take a look at why the Empire failed to conquer Persia each time that they took on the Empire. The first clash between the Ottomans and Sefafids came in 1514 at the Battle of Calderon, and was fought on the soil of Iranian Azerbaijan. Salim I had just taken control of the Ottoman Empire after a secession dispute and feared that a growing Shiite militia group who had supported his rivals would now stir up a new conflict in the name of the Sefafid Shah Ismail. In response, Salim declared war on the Persians and began a march into eastern Anatolia. Predictably, the draining trek quickly began to reduce the morale of the Ottoman troops, in addition to the uneasiness from many who did not like the idea of going to war with fellow Muslims. Meanwhile, alerted of the declaration, Ismail worked to wrap up his current conflict in the east against the Uzbeks in hope of avoiding a two-front war. The Sefafids finally arrived in Calderon after enacting a scorched-earth policy in the west to weaken the Ottoman advance, and just as the Janissaries began to express their clear discontent with Salim and the overall campaign, the armies eventually clashed on August 23rd, and more advanced weaponry, planning, and training carried the Ottomans to victory, and a few weeks later, the Sefafid capital of Tabriz, which they raided and captured. They next seized territories in northern Mesopotamia and eastern Anatolia, and may have pushed even further into Persia if not for growing frustrations from within the Janissaries. Salim subsequently opted to return to Constantinople to appease his men, and while victory was obtained, it was clear already that the journey into Persia would not be an easy obstacle for the Ottoman troops to overcome if extended. Next came the Ottoman-Sefafid War in 1532 through 1555. This time, the conflict began from mutual territorial disputes and included an effort from the Persians to form an alliance with the Europeans, particularly the Habsburgs, to try and correlate an attack on the Ottomans from both sides at once. Still, the Ottomans found quick success as they attacked Sefafid-Iraq and recaptured the Sefafid capital. Catching wind of the Habsburgs-Persian alliance, the Ottomans now formed friendly ties with the Habsburg rivals in France and formed a Franco-Ottoman alliance, which led to further Ottoman expansion in eastern Anatolia and the surrounding Persian territories with the help of a French ambassador. The war was eventually concluded with the Peace Treaty of Amasya, which confirmed most of the Ottomans' territorial gains but did return Tabriz to the Sefafids. While this war was yet again a triumph for the Ottoman Empire, they were so far unsuccessful in taking any Persian lands within modern-day Iran, aside from the temporary claims to the capital. Pushing deeper into Persia remained too taxing. Nonetheless, in 1578, another war broke out between the Ottomans and Sefafids after the Uzbeks reached out to the Ottomans to offer a collaboration that would force the Sefafids to fight a two-front war once more. Despite hesitation from the Sultan, once the Uzbeks made their move, the Ottomans followed by attacking the Sefafid-controlled Caucasus. Once again, they managed to seize Tabriz and also captured multiple Caucasian towns along the way. The Sefafids were struggling to maintain both fronts but found a streak of luck when the Uzbeks were forced to withdraw to deal with their own political issues elsewhere. This triggered some of the formerly conquered rulers under the Ottomans to defect to the Sefafids, but none of this was enough to slow the Ottoman momentum, and by the conclusion of the war with the Treaty of Istanbul in 1590, Sefafid territories in the Caucasus, Anatolia, Mesopotamia, and parts of the west of Persia had fallen to the Ottomans. Still, it's important to note that Ottoman progress stayed in the west of Persia, just across their own border. Further campaigns going deeper into today's Iran had yet to materialize, likely due to the practicality of it. Angered anyway by the Ottomans' recent consolidation, the Sefafids now attacked their rival in 1603 with the goal of recapturing their lands while the Ottoman Empire was stretched thin by internal conflicts. The Jalali Revolts, the conflict this time raged on until 1618, generally considered to have occurred in two stages and resulted in the successful recapture of part of the Sefafid's old territories in the Caucasus and Persia itself. Throughout the 1700s, repetitive battles continued to break out between the Ottomans and Sefafids, and then the Ottomans and Afsharid Persian Empire and Zand Dynasty, but still, no real progress could be made on behalf of the Ottoman expansion deeper into Persia. The final major conflict came in the Ottoman-Persian War of 1821 through 1823 and pitted the Ottomans against the Persian-Qajar Empire. The warfare mostly occurred around Eastern Anatolia and the Turkish-Persian border, which again meant that the Ottomans did not attempt to go further into Persia for a real conquest. The result of this final clash was pretty lackluster, and no territorial changes were even made. Additionally, by this point, conflict with the nearby European powers was increasing, and the centuries of Ottoman-Persian Wars had taken its toll on both sides. This was also the final century of the Ottoman Empire's existence. Becoming known as the Sick Man of Europe, the Ottomans were in no position to try and undertake such a massive invasion by now, and especially one that would be as tiring as a Persian conquest would be. There was simply no motivation nor opportunity to do so at this point, and previously there lacked a proper chance as well. The Ottoman-Persian Wars demonstrated Persia's ability to fight off the Ottoman Empire, even just at the border, and in some instances even showed clearly how the Janissaries felt about the difficult journey just to enter Persia, particularly when the Persians used a scorched earth policy, as they often did against the Ottomans. The religious rivalry and other factors that may have motivated the Ottomans to want to try and capture Persia just would not have been enough to overcome the reality of the situation. The terrain was too hard to trek for long periods, and with insufficient supplies, it was nearly impossible to enter Persia in such a way that the Ottoman forces would be able to rest before clashing with any Persian troops. It would have been almost a waste entirely, given the fact that the Persians could recapture any seized territories as the Ottomans tried to navigate through the mountain ranges to return home, and the Persians were not a weak nation under any of the empires and dynasties that the Ottomans faced. This on top of conflicts with the Europeans overlapping, and internal conflicts within the Ottoman Empire itself, all in all, made a conquest of Persia very low on the list of risks the Ottomans should or would take. By the time the series of Ottoman-Persian wars ended, it was clear that even if there had been an opportunity for such an endeavor, the time had passed, and by now, the Ottomans would not conquer Persia.