Usually one is called the descendants of the other, but this is not entirely true. The relationship between them is much more complex, in connection with which it is not necessary to unquestioningly assert that the Ottomans descended from the Seljuks. Although close, they are a separate people with their own political history and a special ethnic core.
Ottoman and Seljuk
Let’s discuss how they divided.
It all started east of the Caspian Sea a thousand years ago. At that time, the Oghuz Yabgu state was in decline. During several centuries of prosperity, the number of nomads had grown so much that there was no longer enough land for everyone. This led to feuds, during which in 986 the family of Prince Seljuk and his retinue moved to Jend. The city was located in the southern part of modern Kazakhstan and was the first settled settlement on the border of the steppe.
Here they converted to Islam following the example of their subjects. And on this basis they refused to pay tribute to the Oguz rulers, who were still pagans. Those in response intensified their attacks, and the grandsons of Seljuk in the 1030s were forced to lead their people further beyond the Amu Darya to the territory of settled countries.
Just before this, the region had been conquered by the Afghan Ghaznavid dynasty from the Tajik Samanid state, which fell. The conquerors were of Karluk origin, that is, they belonged to a different line of Turks, unlike the Oghuz.
Whether tribal prejudices played their role, or something else, but the Afghans refused to give land to the refugees, who asked to serve them and had already helped them once in military campaigns. Therefore, in 1040 near the ancient city of Merv (modern Turkmen Mary) the battle of Dandanakan took place.
Brothers Togrul-bek and Chagri-bek, grandsons of Seljuk, defeated the enemy and founded their sultanate in Khorasan. The descendants of their warriors, as well as the Oghuz, who migrated during the 11th century to join the successful conquerors, were then called Seljuks. It is common among the Turks for a new nation to be named after its leader: Nogai, Uzbek, Seljuk, Ottoman.
Within a short time, the Seljuks conquered most of western Asia. But in Anatolia, the Byzantine Empire was strong. Although Sultan Alp Arslan defeated it at the Battle of Mancikert in 1071, he did not conquer the land and retreated to his own country.
This was taken advantage of by his rebel third cousin named Suleiman ibn Kutulmysh. His father and grandfather claimed the throne of the Seljuk Empire, but lost the power struggle to the Alp Arslan line. First as a mercenary for the Greek emperors, then as a participant in the civil war, he seized lands in Asia Minor and proclaimed the establishment of the Sultanate of Rum. Historians also call it Konya after the city that became the capital a little later.
Yes, the Conians were the same as the Seljuks. But they never obeyed the main sultans, but instead were hostile to them. Their fate always hung in the balance, for they had to fight both the Byzantines, the Crusaders, and their Seljuk brothers. But at the end of the 12th and beginning of the 13th century their situation stabilized, and then the Mongol invasion happened.
The first blow was taken by the Central Asian power of the Khorezmshahs, a joint “project” of the Oghuz and Kipchak tribes, who dominated over the sedentary Iranians. They were also different ethnoses of medieval Turks, but that was not the case at the time. After the defeat, the nomads were forced to flee, and traveled across Asia.
We are interested in the Kayi tribe, from which the Oguz Yabgu (khans) once originated. At that time it disintegrated, and the survivors scattered wherever they could. 500 tents (i.e. 500 families or 500 warriors) led by a certain Ertogrul went to Anatolia. There they aided in battle a Konian sultan who was fighting the Mongols, and were given land by him to settle on the Byzantine border.
These 500 soldiers are considered to be the founders of the Ottoman Empire, and their leader the founder of its dynasty. Historically, these people were not Seljuks, although they were related to them through the Oghuz. They were not Muslims at that time — at least we do not know the Islamic name of Ertogrul. But then converted to the new faith and adopted a common identity. In addition, in the late 13th and early 14th century, Turkic warriors-ghazi, who wanted to fight against Christians, arrived en masse in the principality they founded.
Osman, the son of Ertogrul, still paid tribute to the Mongols, but eventually gained independence and his people were called Ottomans. His descendants crossed the Bosporus and began the conquest of Byzantine and Slavic lands in Europe. They seriously expanded their Asian possessions, but further expansion was interrupted by Tamerlane. In 1402 the Battle of Angora took place in Anatolia, during which Sultan Bayezid Lightning and his sons were captured.
This led to many years of civil war, when many Turkic tribes got out of control. Apparently, this fact greatly influenced the Ottoman political tradition. Henceforth, the sultans did not rely on Turkic nomads, but on the recently Islamized inhabitants of the cities and the Janissary Corps they had created.
Now these people were called Ottomans, while the government did not trust the free Turks. They retained their former way of life for a very long time, and later became known as Jurüks. This word is formed from the verb “to walk” and by meaning means “nomads”.
Many Jurüks converted to Shi’ism or other unorthodox Islamic faiths, such as Bektashism and Alevism, during the late Middle Ages. In this regard, they were culturally influenced by their tribesmen in Persia, who were the same people, adhered to nomadism and Shiite religion. Even the core of the modern Azerbaijani ethnos was formed precisely by emigrants from Central Anatolia.
Yurüks, descendants of the Seljuks
So, Seljuks and Ottomans are not the same thing at all. Even at the dawn of the Ottoman Empire, they were somewhat different tribes, though descended from the Oghuz. But then the content of the term changed, and not natural Turks, but Turkish-speaking new Muslims began to be called so. They were mostly Byzantine converts.