One of Selim's first challenges as Sultan involved the growing tension between himself and Shah Ismail, who had recently brought the Safavids to power and had switched the Persian state religion from Sunni Islam to adherence to the Twelver branch of Shia Islam.
By 1510 Ismail had conquered the whole of Iran and Azerbaijan, southern Dagestan (with its important city of Derbent), Mesopotamia, Armenia, Khorasan, Eastern Anatolia, and had made the Georgian kingdoms of Kartli and Kakheti his vassals.
He was a great threat to his Sunni Muslim neighbors to the west.
In 1511 Ismail had supported a pro-Shia/Safavid uprising in Anatolia, the Şahkulu Rebellion.

In 1514 Selim I attacked Ismail's kingdom to stop the spread of Shiism into Ottoman dominions.
Selim and Ismā'il had exchanged a series of belligerent letters prior to the attack.
Selim I defeated Ismā'il at the Battle of Chaldiran in 1514.
Ismā'il's army was more mobile and his soldiers better prepared, but the Ottomans prevailed due in large part to their efficient modern army, possession of artillery, black powder and muskets.
Ismā'il was wounded and almost captured in battle, and Selim I entered the Iranian capital of Tabriz in triumph on 5 September,
but did not linger.
The Battle of Chaldiran was of historical significance: the reluctance of Shah Ismail to accept the advantages of modern firearms and the importance of artillery proved decisive.
After the battle, Selim, referring to Ismail, stated that his adversary was: "Always drunk to the point of losing his mind and totally neglectful of the affairs of the state".
One of Selim's first challenges as Sultan involved the growing tension between himself and Shah Ismail, who had recently brought the Safavids to power and had switched the Persian state religion from Sunni Islam to adherence to the Twelver branch of Shia Islam. By 1510 Ismail had conquered the whole of Iran and Azerbaijan, southern Dagestan (with its important city of Derbent), Mesopotamia, Armenia, Khorasan, Eastern Anatolia, and had made the Georgian kingdoms of Kartli and Kakheti his vassals. He was a great threat to his Sunni Muslim neighbors to the west. In 1511 Ismail had supported a pro-Shia/Safavid uprising in Anatolia, the Şahkulu Rebellion.
In 1514 Selim I attacked Ismail's kingdom to stop the spread of Shiism into Ottoman dominions. Selim and Ismā'il had exchanged a series of belligerent letters prior to the attack. Selim I defeated Ismā'il at the Battle of Chaldiran in 1514. Ismā'il's army was more mobile and his soldiers better prepared, but the Ottomans prevailed due in large part to their efficient modern army, possession of artillery, black powder and muskets. Ismā'il was wounded and almost captured in battle, and Selim I entered the Iranian capital of Tabriz in triumph on 5 September,
but did not linger. The Battle of Chaldiran was of historical significance: the reluctance of Shah Ismail to accept the advantages of modern firearms and the importance of artillery proved decisive. After the battle, Selim, referring to Ismail, stated that his adversary was: "Always drunk to the point of losing his mind and totally neglectful of the affairs of the state".
Selim I