evidence: Since the Ottoman–Persian Wars of the 16th and 17th centuries, Iran (known as "Persia" prior to 1935) and the Ottomans fought over Iraq (then known as Mesopotamia) and full control of the Shatt al-Arab until the signing of the Treaty of Zuhab in 1639, which established the final borders between the two countries. The Shatt al-Arab was considered an important channel for both states’ oil exports, and in 1937, Iran and the newly independent Iraq signed a treaty to settle the dispute. In the same year, Iran and Iraq both joined the Treaty of Saadabad, and relations between the two states remained good for decades afterwards. [...] In the 1975 Algiers Agreement, Iraq made territorial concessions—including the Shatt al-Arab waterway—in exchange for normalized relations. In return for Iraq recognizing that the frontier on the waterway ran along the entire thalweg, Iran ended its support of Iraq’s Kurdish guerrillas. Iraqis viewed the Algiers Agreement as humiliating. Tensions between Iraq and Iran were fueled by Iran’s Islamic revolution and its appearance of being a Pan-Islamic force in contrast to Iraq’s Arab nationalism. Despite Iraq’s goals of regaining the Shatt al-Arab, the Iraqi government seemed to initially welcome Iran’s Revolution, which overthrew Iran’s Shah, seen as a common enemy. It is difficult to pinpoint when tensions began to build.