The disappointment over the peace treaty after the Balkan wars, caused Bulgaria to enter World War I on the side of the Central Powers.
After staying neutral during the first year of the war, the country
attacked Serbia in the autumn of 1915. The Serbian army was defeated in
a few days, and the Bulgarians advanced through Macedonia towards
Salonika which was the Entente bridgehead on Balkan. However, the
German supreme command wanted to maintain a front on Balkan to bind
Entente troops otherwise available against the Germans on the west
front. The Bulgarian advance was thus stopped, and a front line
extending from Albania to Thrace was established.
In the
autumn of 1916 Romania entered the war on the side of the Entente. The
Bulgarian supreme command only had one army group left to engage
against the Romanians. However, these forces considered the fighting as
a war of liberation for their people in Dobrudja, occupied by Romania
only three years before. Both the Romanian army and several Russian
supporting divisions were beaten in only two months. Early December the
Bulgarian forces supported by German units advanced into Bucurest, the
capital of Romania.
A long-lasting embargo
from the entente side caused suffering and social unrest in Bulgaria.
In September 1918 several Bulgarian divisions in Macedonia deserted and
marched towards Sofia. However, the fatigued and poorly organised
rebels did not succeed in breaking through the loyal defence forces
surrounding the capital, supported by German troops, and the rebellion
was put down October 2, 1918.
In the meantime,
however, the government had asked for a cease-fire with the Entente.
The truce was signed September 29 in Salonika, demanding full retreat
of all Bulgarian forces and occupation of strategically vital areas by
Entente troops.
Later, in the peace treaty of Neuille November 1919
Bulgaria lost further territories to it's neighbors, including Thrace
and the access to the Aegean Sea. Having led the country into two
national disasters since 1913, King Ferdinand was forced to abdicate
October 3, 1918. His son ascended the throne as Boris III.