The Parliamentary Assembly, which was annulled in 1918, convened again in January 12, 1920 and ratified Misak-ı Milli (National Contract) on January 28. On March 4, 1920, and the invasion of Istanbul was approved at London Conference. In March 4, the postal administration office was invaded. On the night of March 15, the action of general invasion was triggered. In the morning, a large number of soldiers invaded Istanbul and important parts of the city were taken under control. In late morning, the city was completely occupied. And in the afternoon English soldiers raided the Parliament Assembly building. And on April 11, the Parliamentary Assembly was closed. About 150 politicians were exiled to Malta. During this period, some secret organizations were formed in Istanbul and started agitating for freedom. Patrolling Society, Mim Group and National Defense organization were the most influential secret organizations in Istanbul during that period. They organized demonstrations and carried out activities like handover of arms, soldiers and munitions and exchanging secret information.
On October 9, 1920, Turkish soldiers entered Izmir’s boundaries led by supreme national leader Mustafa Kemal Atatürk. This event started the independence process for Istanbul. With the Mudanya Agreement signed on October 11, it was agreed that the invading forces would leave Thrace gradually. The Turkish Grand National Assembly that convened in Ankara declared the Ottoman dynasty be abolished in November 1, 1922. Therefore, even though Istanbul remained the legal capital until October 1923, it was no longer the actual capital. On November 16 Sultan Vahdettin left Istanbul.
In November 4, 1923, Istanbul was completely free of invading forces. Therefore, the second invasion of Istanbul by Europeans after the Latin invasion of 1204 was terminated.