The abolition of the Ottoman Caliphate
The Turkish National Assembly, led by Mustafa Kemal, issued the decision to abolish the caliphate and exile the last caliph, ʿAbd al-Majid II. With it fell the last unifying symbol of the Muslims after some thirteen centuries of the caliphate.
The Ottoman Caliphate had weakened for centuries, until the state was defeated in the First World War and Istanbul was occupied. The caliphate was then stripped of the sultanate in 1922, and ʿAbd al-Majid II remained a nominal caliph without rule.
On 28 Rajab 1342 AH (3 March 1924) the Grand National Assembly in Ankara voted to abolish the office of the caliphate definitively and expel the House of Osman from Turkey, so ʿAbd al-Majid II left for Switzerland on the next morning's train.
The Muslim world was shaken by the news; caliphate congresses were held in Cairo and Makkah to no avail, and the event remained a turning point in modern history, after which the Ummah split into nation-states — many researchers date from it the beginning of an entirely new age.
Note — differing reports on the date: The decision was issued on 3 March 1924, which, according to calendar differences, corresponds to 27 or 28 Rajab 1342 AH — the 28th of Rajab being the more common in references.