Orhan, also known as Orhan Gazi or Orkahn (born in 1285 and passed away in 1359), was the second leader of the Ottoman Empire (the title Sultan was not used until 1383), and his reign lasted from 1326 to 1359. He occupied most of the western Anatolia and married the daughter of Byzantine Emperor John VI, but also helped John VI overthrow John V as Byzantine Emperor, thus accelerating the decline of the Byzantine Empire. In 1354, his eldest son Suleiman Pasha occupied Gallipoli, opening up a bridgehead for the Ottoman Empire on the European continent.

After the death of Ottoman I, his son Ulhan came to power. Ulhan was already designated as the heir by his father before Ottoman's death. Ulkhan originally intended to divide the empire among his brother Alaedin, but Aladdin opposed the division and insisted that Ulkhan be the ruler of the country, while he himself only demanded taxes and profits for one village. Urhan therefore said to Aladdin, "Brother, since you are unwilling to accept the sheep and cattle I give you, you should at least become the shepherd of my subjects, and you should become my great vizier." According to Ottoman historians, in Turkish, the name of great vizier originally meant "responsible person". Aladdin mainly manages the civilian and military institutions of the country, but he rarely leads his own troops.
Some experts believe that with the help and advice of Aladdin, Ulkhan stopped paying tribute to the rulers of Konya, began issuing his own currency, and began using his own name in public prayers. But most experts believe that Ottoman had already introduced these measures. Aladdin established many laws unique to the Ottoman Empire that lasted for many centuries, and he also began to establish a regular army and provided its expenses. At his suggestion, Ulkhan (not Murad I) established the new army of Türkiye.

Aladdin's military management can be said to have laid the foundation for the rise of the Ottoman Empire. He established a regular and regularly paid army, including well disciplined infantry and cavalry. This measure predates the fifteen permanent missions established by King Charles VII of France by a full century.
Ulkhan's predecessors summoned his vassal states and volunteers during the war, and after the war, these armies were disbanded and returned home. Aladdin decided that in order to increase the possibility of future victory, he must establish a salaried infantry army that can always launch attacks. This army is divided into teams of ten, a hundred, and a thousand people. Their salary is quite high, and their arrogance quickly brought some troubles to Ulhan. He needed a measure to control this army, so he discussed it with Aladdin. They established the Guard Army (Sudan's personal soldiers) for this purpose. Later, this guard army boldly became a major enemy of Christians and also a great concern for the Ottoman Sultan. Later, the Ottoman Sultan disbanded this guard army.
Ulhan selected a thousand boys from the Christians in the occupied areas, and the following year he selected another thousand to undergo military training and form the Guard. This practice continued in the Ottoman Empire for hundreds of years until Murad IV ceased in 1648.

Ulkhan expanded outward from the first year of his rule, using the war resources provided by his brothers to accelerate his expansion. In 1330, he surrounded the second largest city of the Byzantine Empire, Nicaea (Iznik). Ulkhan's eldest son commanded the siege. Since then, the Ottoman Empire has constantly defeated Byzantium and other rulers of Türkiye (especially the leaders of Nicia) who opposed the Ottoman Empire. Nicaea was incorporated into its territory by Ulkhan. In 1336, almost the entire northwest of Anatolia was occupied. Cities such as Bursa, Nice, and Bergamos became important fortresses of the Ottoman Empire.

Afterwards, the Ottoman Empire entered a 20-year period of peace, during which Ulkhan devoted himself to improving the civilian and military management institutions within the empire, constructing mosques and schools, and constructing many contemporary public buildings that still exist. He gradually absorbed the occupied Anatolia as part of the Ottoman Empire, which was very important for the long history of the Ottoman Empire. Later sultans of the Ottoman Empire, especially in their conquest of Europe, overlooked this experience. Contemporary Anatolia is regarded as the heartland of Türkiye, which is related to the infiltration of the Seljuk Empire into this region before the establishment of the Ottoman Empire, but also to the wise policies of Ulkhan and his successors.
The friendly relationship between Ulkhan and Byzantine Emperor Andronicus III and his successors (although there were some interruptions) led to a 20-year peace for the Ottoman Empire.
The Ottoman Empire's army participated in the Byzantine civil war as federalists, and they increasingly fought in Europe. In 1346, John VI recognized Ulkhan Anatolia as the most powerful ruler. Despite being very different from his daughter and having a huge grade difference (Ulhan was already 60 years old at the time, while John's daughter was still a young girl), he married his daughter to Ulhan in the hope of gaining long-term support from the Ottoman Empire.
Byzantine writers detailed the grand wedding between Ulkhan and Theodora. But the following year, after Ulhan visited John in the Asian part of Constantinople, some of his followers crossed the Black Sea and looted some cities in Thrace. In the end, all these armies were defeated by Byzantium.

Shortly thereafter, the armed conflict between Ulkhan's army and John's army led to a war between Venice and Genoa that affected almost all areas along the Mediterranean coast, ultimately leading to the Ottoman Empire's invasion of Europe.
Genoa has a stronghold called Galata in the European part of the Bosphorus Strait. Here, Genoa's fleet often conflicts with its competitors' fleets. Ulkhan harbored great hatred towards Venice for two reasons. The first Venetian fleet often harassed the coastal provinces of Ulkhan. Secondly, when Ulkhan sent envoys to Venice, Venice was very arrogant towards him, as if he were a chieftain of a barbaric tribe. Venice allied with John VI, so Ulkhan sent troops to Galata to support Genoa and another anti John son-in-law (later John VI).
In 1356, in this chaos, Ulkhan's eldest son Suleiman took a bold action to obtain a permanent stronghold for Türkiye on the European side of the Straits.
The authors of the Ottoman Empire often remained silent about their previous futile expansion into Europe, while they greatly exaggerated Suleiman's actions.
Suleiman, with only 39 soldiers, hid in a boat in Genoa and crossed the sea to ambush the castle of Gallipoli. After their success, they quickly transported reinforcements to the castle, and within three days, the number of soldiers inside the castle reached 3000.
At this time, John V was engaged in a fierce battle with his civil war enemies. He not only failed to drive out the invaders, but also sought help from Ulhan. Ulkhan had already given up his support for his father-in-law and began supporting John VI. He ordered Suleiman to command the Ottoman army and increase his troops by 10000. After defeating the enemy, Suleiman did not hand over the area he occupied to his allies, but instead stayed there himself. John VI offered Suleiman ten thousand gold coins in exchange for the territories occupied by Suleiman, and Suleiman agreed. But at this moment, a major earthquake broke out in Thrace, causing the walls of many cities to collapse.

The Turks believed that this was the help of God, who paved the way for them to Europe. Suleiman's two generals immediately occupied the important city of Gallipoli, crossing the destroyed city walls without encountering any resistance from the paralyzed residents. Until today, the tombs of these two generals are still there.
Suleiman heard that his army had occupied Gallipoli and no longer intended to abandon the place he had occupied. He began to immigrate to these places in large numbers, and Turks and Arabs who entered occupied this place. The city walls of Gallipoli were rebuilt, and heavy troops were stationed inside the city. Suleiman also took the opportunity to occupy other cities in Thrace, strengthen the defense system there, and send his elite troops to garrison.
John VI protested to Ulhan, who replied that it was not the army that opened these cities for his son, but God opened them through earthquakes. John said: The question is not how Türkiye's army entered these cities, but whether they have the right to occupy them. Ulhan replied that he needs time to consider this issue. Later, he made suggestions on how to rebuild these cities, but there is no doubt that he does not want to give up the advantage he gained through the opportunity.
Gallipoli became one of the bases of the Ottoman Empire in Europe and a subject of mutual criticism between John V and John VI. And both John also sought help from Ulhan, who sometimes helped this one and sometimes helped that John according to his own interests. He is actually the true enemy of the two.

Suleiman passed away three years after occupying Gallipoli, and his most hopeful son Suleiman died before him. Suleiman fell off his horse while hunting eagles and died from injuries. Suleiman was buried in Bursa, but Ulkhan ordered a tomb to be built for him on the coast of the Bosphorus Strait.
Ulkhan died in 1359 at the age of 75 and ruled for 33 years. During his reign, the most important civilian and military management institutions of the Ottoman Empire were established. He not only captured the Ottoman Empire's most important provinces in Asia, but also established a foothold in Europe during his reign.