Many non-sovereign monarchs either lost their thrones through deposition by a coup d'état, by a referendum which abolished their throne, or chose to abdicate during the 20th century.
German royalty was abolished in the aftermath of World War I.
A
Abuja
Malam Awwal Ibrahim, emir of Abuja (in Nigeria), deposed or abdicated 1994, restored 2000.
Aceh Darussalam
Sultan Kehalarat Deelat Nyang Meuha Meulia Paduka Seri Baginda Sultan Berdaulat Zilulahil Filalam Alaudin Muhammad Daud Shah (His Majesty Sultan Muhammad Daud Shah) of Aceh (in Indonesia) surrendered to the Netherlands following the arrest of the Queen and Queen Mother in 1903.
Agaie
Muhammad Nkochi Attahiru, emir of Agaie, deposed 1994, restored 2001.
B
Baroda
Farzand-i-Khas-i-Daulat-i-Inglishia, Shrimant Maharaja Sir Pratapsinhrao Gaekwad, Sena Khas Khel Shamsher Bahadur, Maharaja of Baroda, deposed 1951.
Bharatpur
Maharaja Shri Brijendra Sawai Brijendra Singhji Bahadur Bahadur Jang, Maharaja of Bharatpur was deposed in 1971.
Bhopal
Sikander Saulat, Iftikhar ul-Mulk, Nawab Sultan Kaikhusrau Jahan Begum Sahiba, Nawab Begum of Bhopal, abdicated in 1926.
Bone state
La Pawowoni Karaeng Segeri Arumpone of Bone was deposed in 1905.
Haji Andi La Mappanjuki Karaeng Silayar Sri Sultan Ibrahim ibnu Sultan Husain Arumpone of Bone abdicated 1946, was restored 1950, and reigned again until 1960.
Andi Pabenteng Arumpone of Bone was deposed in 1950.
Buffalo Point
Warren Thunder, chief of Buffalo Point, deposed 1969, died 1973.
Bugabula
William Wilberforce Kadhumbula Nadiope III, Omukama of Bugabula, deposed by the Ugandan government in 1967, died 1973
Buganda
Major-General H.H. Edward Frederick William David Walugembe Mutebi Luwangula Mutesa II Kabaka of Buganda was deposed by the abolition of the Ugandan kingdoms on September 8, 1967.
Buhweju
Ndagara, Omukama of Buhweju, deposed 1901.
Buleleng
Sri Ratu Anak Agung g Nyoman Panji Tisna Raja of Buleleng abdicated 1947 and was reinstalled in 1950.
Sri Ratu Anak Agung Panji Sakti II Raja of Buleleng abdicated in 1950.
Bukhara
Emir Mohammed Alim Khan was deposed in 1920 when his lands were taken over by Bolsheviks.
Busoga
William Wilberforce Kadhumbula Nadiope III, Isebantu Kyabazinga of Busoga, deposed by the Ugandan Government in 1967.
C
Caliphate
Caliph Abdul Mejid II, cousin of the last Ottoman Sultan, was deposed in 1924.
Champasak
Bua Laphan Ratsadany, prince of Champasak 1900–1904, was deposed when the principality was abolished on November 22, 1904.
Chisasibi
Violet Pachanos, chief of Chisabibi 1989–1995, deposed or abdicated 1995, restored 1999, reigned until 2001.
Cochin
Sir Sri Rajarshi Rama Varma, Maharaja of Cochin, abdicated his throne in 1914 owing to ill-health and differences with the British Empire.
Rama Varma Parikshith Thampuran, Maharaja of Cochin, signed the instrument of accession to the Dominion of India thus ending the executive political role. Cochin was merged with Travancore to form Travancore-Cochin Union from 1 July 1949.
D
Dewas
Kshatriya Kulavatana Sena Sapta Sahasri Senapati Pratinidhi, Meherban Shrimant Maharaja Sir Vikramsinhrao Tukojirao (Nana Sahib) Puar, Maharaja of Dewas, abdicated in 1947.
G
Gojjam
Negus Tekle Haymanot Tessema of Gojjam, died in 1901 and his kingdom was divided and incorporated into the Empire of Ethiopia.
Gowa
Andi Ijo Daeng Mattawang Karaeng Lalolang Paduka Sri Sultan Muhammad 'Abdu'l Kadir Aid ud-din ibnu Sultan Muhammad Tahir Muhib ud-din, Sultan of Gowa, was deposed by the Indonesian republic in 1960.
H
Hejaz
King Ali of Hejaz, deposed by Saudi military forces in 1925.
I
Igara
Musinga, Omukama of Igara, deposed 1901.
J
Jimma
The last King of Jimma, Abba Jifar II, died and, on 12 May 1932, the Kingdom of Jimma was incorporated into the Empire of Ethiopia.
K
Khiva
Khan Abd Allah Khan was deposed 1920; his lands were taken over by Bolsheviks.
Kokang
Yang Guo Zhen Hkun Lu Kwan, Heng of Kokang—1919.
Sao Edward Yang Kyein Tsai, Saopha of Kokang, deposed by Burma, 1959.
Kubu
Sharif 'Abbas ibni al-Marhum Sharif Hasan 'Ali al-Idrus, Yang di-Pertuan Besar of Kubu, was deposed in 1911.
Sharif Muhammad Zainal Idrus ibni al-Marhum Sharif Ismail al-Idrus, Tuan Besar of Kubu, abdicated in 1921.