After Stamboliyski was overthrown in a coup in 1923, Boris recognized the new government of Aleksandar Tsankov, who harshly suppressed the Bulgarian Communist Party and led the nation through a brief border war with Greece.

Tsankov was removed from power in 1926, and a series of prime ministers followed until 1934, when the corporatist Zveno (Bulgarian: Звено) movement staged a coup and outlawed all political parties.

Bulgaria then received large portions of Yugoslav Macedonia, Pirot County in eastern Serbia and Greek Thrace, which were key targets of Bulgarian irredentism.

As part of the Holocaust, Bulgarian authorities deported most Jews from occupied Greek and Yugoslav territories and transferred them to the German extermination camp of Treblinka.

In 1942, Zveno, the Agrarian National Union, the Bulgarian Communist Party, and other far-left groups united to form a resistance movement known as the Fatherland Front, which went on to overthrow the government in 1944.

In February 1896, his father paved the way for the reconciliation of Bulgaria and Russia with the conversion of the infant Prince Boris from Catholicism to Eastern Orthodoxy, a move that earned Ferdinand the frustration of his wife, the animosity of his Catholic Austrian relatives (particularly his uncle Franz Joseph I of Austria) and excommunication by Pope Leo XIII.

Nicholas II of Russia stood as godfather to Boris and later met the young boy during Ferdinand's official visit to Saint Petersburg in July 1898.

Boris worked hard to smooth the sometimes difficult relations between Field Marshal Mackensen and Lieutenant General Stefan Toshev, the commander of the Third Army.

Two days later, a bomb killed 150 members of the Bulgarian political and military elite in Sofia as they attended the funeral of a murdered general in the Saint Nedelya Church terror assault.

[4] With the rise of the "King's government" in 1935, Bulgaria entered an era of prosperity and astounding growth, which deservedly qualifies it as the Golden Age of the Third Bulgarian Kingdom.

"[7] During a visit to the United Kingdom in 1937, Boris made international news for taking the throttle of a London Midland Scotland Railway Coronation Class steam locomotive.

In March 1941, Boris allied himself with the Axis powers, thus recovering most of Macedonia and Aegean Thrace, as well as protecting his country from being crushed by the German Wehrmacht like neighboring Yugoslavia and Greece.

[11][12] Despite this alliance, and the German presence in Sofia and along the railway line which passed through the Bulgarian capital to Greece, Boris was not willing to provide full and unconditional cooperation with Germany.

They held closed-door meetings and ended with a secret agreement signed on 22 February 1943 for the deportations of 20,000 Jews – 11,343 from Aegean Thrace and Vardar Macedonia, and 8,000 from Bulgaria proper.

[citation needed] The initial roundups began on 9 March 1943, during that month, Bulgarian military and police authorities deported 11,343 Jews from the Bulgarian-occupied regions of Vardar Macedonia, Pomoravlje in occupied Yugoslavia and Aegean Thrace to Auschwitz-Birkenau and Treblinka.

On the morning of 9 March, a delegation from Kyustendil, composed of eminent public figures and headed by Dimitar Peshev, the deputy speaker of the National Assembly, met with Interior Minister Petur Gabrovski.

In fact, Gabrovski's decision was not taken on his own "personal initiative", but had come from the highest authority – Tsar Boris III, who decided under pressure to temporarily stop the deportation of the rest of the Jews.

[16] Aware of Bulgaria's unreliability on the Jewish matter, the Nazis grew more suspicious about the quiet activities in aid of European Jewry of an old friend of Tsar Boris, Monsignor Angelo Roncalli (the future Pope John XXIII), the Papal Nuncio in Istanbul.

Upon returning home, Boris ordered able-bodied Jewish men to join hard labor units to build roads within the interior of his kingdom.

Boris continued the cat-and-mouse game that he had long been playing; he insisted to the Nazis that Bulgarian Jews were needed for the construction of roads and railway lines inside his kingdom.

The request caused a public outcry, and a campaign whose most prominent leaders were Parliament's deputy speaker Dimitar Peshev[19] and the head of the Bulgarian Orthodox Church, Archbishop Stefan, was organised.

[20] On 30 June 1943, Apostolic Delegate Angelo Roncalli, the future Pope John XXIII, wrote to Boris, asking for mercy for "the sons of the Jewish people."

[17] An excerpt from the diary of Rabbi Daniel Zion, the spiritual leader of the Jewish community in Bulgaria during the war years, reads: Do not be afraid, dear brothers and sisters!

When I entered, my words were: "Yes, my brethren, God heard our prayers ..."[17]Most irritating for Hitler was the Tsar's refusal to declare war on the Soviet Union or send Bulgarian troops to the Eastern Front.

[25] His son Simeon Saxe-Coburg-Gotha did not deny this version, but pointed out as probable the hypothesis that the USSR was also interested in the Tsar's death, in which case the NKVD intervened.

[26][27] Princess Marie Louise of Bulgaria stated in an interview that there was no definite version of what had happened, but that she was convinced that her father had not been poisoned by the Nazis or the British, but by the East.

According to Goebbels, Hitler was convinced that the Italian royal court was the organizer of the poisoning of Boris III, as Princess Mafalda of Savoy, sister of Joan of Bulgaria, was visiting Bulgaria four weeks before the monarch's death and her visit coincided with the events of 25 July 1943,[30][31] the overthrow of the Italian Fascist dictator Benito Mussolini, supported by King Victor Emmanuel III.

[citation needed] A wood carving is placed on the left side of his grave in Rila Monastery, made on 10 October 1943 by inhabitants of the village of Osoj, Debar district.

[62] In July 2003, a public committee headed by Israeli Chief Justice Moshe Bejski decided to remove the memorial because Bulgaria had consented to the delivery of 11,343 Jews from occupied territory of Macedonia, Thrace and Pirot to the Germans.