Romania : Under Bulgarian Occupation.

During the Second Balkan War in 1913, Romania intervened against Bulgaria on the side of Serbia and Greece, annexing Southern Dobrudzha under the Treaty of Bucharest. Subsequently, in 1916, after Romania joined the Entente in World War I, Bulgaria, which was an ally of the Central Powers, waged a successful war campaign against the Romanian, Russian, and Serbo-Croatian forces conquering the entire territory of Dobrudzha as well as the Romanian capital Bucharest (together with forces of Germany and Austria-Hungary).
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1916
Listed in Stanley Gibbons under Bulgaria.
Dobrudja District
Stamps of Bulgaria Overprinted
Unwatermarked
Perf 11.5, perf 14

Commemorates the occupation of the Dobrudja District, these were used
for the Bulgarian Post in the then Romania.
Many errors of lettering in overprint exist, incl
double and inverted opts.