Controversial issues that the Treaty couldn’t solve dominated Turkish foreign policy in the wake of the Conference of Lausanne, while the disagreement over Mosul with Britain was the most heated foreign policy issue between 1923-1926.
Upon the application of Britain, the Mosul dispute was referred to the League of Nations on August 6, 1924, which started discussing it on September 20, 1924, one year after the Treaty of Lausanne was signed. During the talks, the Turkish side repeated their offer of a referendum in Mosul, but Britain, just like before, rejected the idea with insolent excuses like ‘locals being ignorant and not understanding about border issues’.(SOURCE) (The Kurdish people in the region are above such remarks). On September 30, 1924, a decision was made to set up an investigative commission, which defined the borders on October 28, 1924 and established a status quo Turkish-Iraqi border named ‘Brussels Line’. The highlights from the report of the commission that was submitted to the League of Nations on July 16, 1925 were as follows:
When Turkey raised objections to this report, the Council asked the Permanent Court of International Justice in Hague on September 19, 1925 to submit its opinion. This opinion was in line with the wishes of the League of Nations, and despite Turkish protests the Assembly of the League of Nations announced on December 8, 1925 that it adopted the resolution of the Court of Justice. Only a couple of days later, on December 16, 1925, it approved the report of the Investigative Commission and decided that the lands lying to the south of Brussels Line be left to Iraq