War with the Ottoman Empire (1775–1776)
In 1774, the Mamluk governor of the Ottoman province of Iraq, Omar Pasha began meddling in the affairs of his vassal principality of Baban, which since the death of his predecessor Sulayman Abu Layla Pasha in 1762, had fallen more and more under the influence of the Zand governor of Ardalan, Khosrow Khan Bozorg. This made Omar Pasha dismiss the Baban ruler Muhammad Pasha, and appoint Abdolla Pasha as its new ruler. This, and Omar Pasha's seizure of the remnants of Iranian pilgrims who had died during the plague that ravaged Iraq in 1773—and his exaction of payment from Iranian pilgrims to visit the holy Shia places of Najaf and Karbala, gave Karim Khan the casus belli to declare war against the Ottomans.
There were also other reasons for Karim Khan to declare war—Mashhad, where the holy Imam Reza shrine was situated, was not under Zand control, which thus meant that free entry to the sanctuaries of Iraq was of more significance to Karim Khan than it had been to the Safavid and Afsharid shahs. The Zand army was discontent, and sought to restore their reputation after Zaki Khans humiliating blunders on the Hormuz Island. Most importantly, Basra was a prominent trading port, which had surpassed the competing city of Bushehr in Fars in 1769, when the East India Company dropped the city for Basra.
The Zand forces under Ali-Morad Khan Zand and Nazar Ali Khan Zand shortly clashed with the Pasha's forces in Kurdistan, where they kept them at bay, whilst Sadeq Khan, with an army of 30,000, besieged Basra in April 1775. The Arab tribe al-Muntafiq, which was allied with the governor of Basra, quickly withdrew without any effort to reject Sadeq Khan from passing through the Shatt al-Arab, whilst the Banu Ka'b and the Arabs of Bushehr supplied him with boats and supplies.
Suleiman Agha, who was the commander of the fort of Basra, resisted Sadeq Khan's forces with resolve, which made the latter establish an encirclement, which would last over a year. Henry Moore, who belonged to the East India company, assaulted some of Sadeq Khan's stockpile boats, tried to block the Shatt al-Arab, and then departed to Bombay. A few months later, in October, a group of ships from Oman gave supplies and military aid to Basra, which considerably lifted the morale of its forces. However, their combined attack the next day occurred to be wavering—the Omani ships eventually chose to withdraw back to Muscat during winter, in order to avoid further losses.
Reinforcements from Baghdad arrived shortly afterwards, which was repelled by the Khaza'il, a Shia Arab tribe which was allied with the Zand forces. In the spring of 1776, the narrow encirclement by Sadeq Khan had resulted in the defenders being on the fringe of famine—a considerable portion of the Basra forces had deserted Suleiman Agha, whilst the rumours of a possible uprising, made Suleiman Agha surrender on 16 April 1776.
Even though the able Ottoman Sultan Mustafa III (r. 1757–1774) had died and was succeeded by his incompetent brother Abdul Hamid I (r. 1774–1789), and the recent Ottoman defeat to the Russians, the Ottoman response to the Ottoman–Iranian war was unusually slow. In February 1775, before the announcement of the siege of Basra had approached Constantinople, and while the Zagros front was temporarily peaceful, the Ottoman ambassador, Vehbi Efendi, was sent to Shiraz. He reached Shiraz around the same time Sadeq Khan besieged Basra, "but was not empowered to negotiate over this new crisis."
In 1778, Karim Khan had made a compromise with the Russians for a cooperative offensive into eastern Anatolia. However, the invasion never took place due to Karim Khan's death on 1 March 1779, after having been ill for six months, most likely due to tuberculosis. He was buried three days later in the "Nazar Garden", now known as the Pars Museum.
