Why was Bulgaria involved in World War 1?

Answer 1

When World War I began, Bulgaria declared strict neutrality, but the Tsar (the King) and a Germanophile government under Vasil Radoslavov encouraged both sides to bid for Bulgarian intervention. In this contest, the Central Powers (Austria-Hungary and the German empire) could offer far more at the expense of Serbia, Greece, and, later, Romania, than could the Triple Etente (an alliance of Great Britain, France, and Russia), which had to take the interests of its smaller allies into account. During the summer of 1915, when the military balance swung in Germany's favour, Bulgaria committed to the Central Powers and declared war on Serbia on October 1 (October 14). Some of the neutralist and pro-Entente political figures objected, but none went as far as the Agrarian leader Stamboliyski, who threatened the tsar and issued a call for the troops to resist mobilization. For these acts he was arrested and condemned to life imprisonment.

Answer 2

Greece including its northern province of Macedonia which was liberated by Greece from Ottoman foreign occupation in 1912, declared war on the Central Powers, ending three years of neutrality by entering World War I alongside Britain, France, Russia and Italy.