Nationalism and the downfall of colonialism led to the greatest wave of anti-monarchical abolitionist movements the world has ever seen. Guess all of the countries that abolished their monarchy, were annexed by another state resulting in the abolition of their monarchy, or declared independence from a sovereign state or colonial empire with it's own monarch from 1900 to the present.
I did not include Lithuania, Poland and Macedonia since their monarchies were abolished before the designated monarch ever took power.
I also chose not to include the Central African Republic since President Bokassa's self-proclaimed imperial title was never recognized internationally.
I did not include Manchukuo (also known as Manchuria), the puppet state that Emperor Puyi of China governed after he was deposed, since he was not a sovereign, but rather under the authority of the Japanese government.