By the time of the German invasion of Poland and subsequent outbreak of war in September 1939, the Yugoslav Intelligence Service was cooperating with British intelligence agencies on a large scale across the country.
This cooperation, which had existed to a lesser extent during the early 1930s, intensified after the Anschluss.
These combined intelligence operations were aimed at strengthening Yugoslavia and keeping her neutral while encouraging covert activities.
In mid to late 1940, British intelligence became aware of coup plotting, but managed to side-track the plans, preferring to continue working through Prince Paul.
The Special Operations Executive (SOE) office in Belgrade went to significant lengths to support the opposition to the anti-Axis Cvetković government, which undermined the hard-won balance in Yugoslav politics that that government represented.
SOE Belgrade was entangled with pro-Serbian policies and interests, and disregarded or underestimated warnings from SOE and British diplomats in Zagreb, who better understood the situation in Yugoslavia as a whole.

Yugoslavia's situation worsened in October 1940 when Italy invaded Greece from Albania, and the initial failure of the Italians to make headway only increased Yugoslav apprehension that Germany would be forced to help Italy.
In September and November 1940 respectively, Germany forced the Kingdom of Hungary and Kingdom of Romania to accede to the Tripartite Pact.
In early November 1940, Nedić, who believed that Germany would win the war, proposed to the government that it abandon its neutral stance and join the Axis as soon as possible in the hope that Germany would protect Yugoslavia against its "greedy neighbors".
A few days later Prince Paul, having realised the impossibility of following Nedić's advice, replaced him with the ageing and compliant General Petar Pešić.
At the same time, Hitler, recalling Serbia's excellent military performance in the Balkan Wars and World War I, was concerned that the Yugoslav army was strong, and defeating it would necessitate the expenditure of considerable effort.
Despite this, he remained concerned about the threat to the southern flank of his planned invasion of the Soviet Union posed by Greece and Yugoslavia, and aimed for a political resolution of Yugoslavia's status.

On 12 December 1940, at the initiative of the Prime Minister of Hungary, Count Pál Teleki, Hungary concluded a friendship and non-aggression treaty with Yugoslavia.
Although the concept had received support from both Germany and Italy, the actual signing of the treaty did not.
Germany's planned invasion of Greece would be simplified if Yugoslavia could be neutralised.
Over the next few months, Prince Paul and his ministers laboured under overwhelming diplomatic pressure, a threat of an attack by the Germans from Bulgarian territory, and the unwillingness of the British to promise practical military support.
Six months prior to the coup, British policy towards the government of Yugoslavia had shifted from acceptance of Yugoslav neutrality to pressuring the country for support in the war against Germany.

On 23 January 1941, William Donovan, a special emissary of US President Franklin D. Roosevelt, visited Belgrade and issued an ultimatum, saying that if Yugoslavia permitted German troop passage then the US would not "interfere on her behalf" at peace talks.
Around the same time, suspicious of Prince Paul's actions, the British Prime Minister, Winston Churchill, ordered British intelligence services to establish contacts with anti-regime groups in Belgrade.
On 14 February, Adolf Hitler met with Cvetković and his foreign minister and requested Yugoslavia's accession to the Tripartite Pact.
He pushed for the demobilisation of the Royal Yugoslav Army—there had been a partial "reactivation" (a euphemism for mobilisation) in Macedonia and parts of Serbia, probably directed at the Italians.
Hitler also pressed the Yugoslavs to permit the transportation of  German supplies through Yugoslavia's territory, along with greater economic cooperation.
In exchange he
By the time of the German invasion of Poland and subsequent outbreak of war in September 1939, the Yugoslav Intelligence Service was cooperating with British intelligence agencies on a large scale across the country. This cooperation, which had existed to a lesser extent during the early 1930s, intensified after the Anschluss. These combined intelligence operations were aimed at strengthening Yugoslavia and keeping her neutral while encouraging covert activities. In mid to late 1940, British intelligence became aware of coup plotting, but managed to side-track the plans, preferring to continue working through Prince Paul. The Special Operations Executive (SOE) office in Belgrade went to significant lengths to support the opposition to the anti-Axis Cvetković government, which undermined the hard-won balance in Yugoslav politics that that government represented. SOE Belgrade was entangled with pro-Serbian policies and interests, and disregarded or underestimated warnings from SOE and British diplomats in Zagreb, who better understood the situation in Yugoslavia as a whole.
Yugoslavia's situation worsened in October 1940 when Italy invaded Greece from Albania, and the initial failure of the Italians to make headway only increased Yugoslav apprehension that Germany would be forced to help Italy. In September and November 1940 respectively, Germany forced the Kingdom of Hungary and Kingdom of Romania to accede to the Tripartite Pact. In early November 1940, Nedić, who believed that Germany would win the war, proposed to the government that it abandon its neutral stance and join the Axis as soon as possible in the hope that Germany would protect Yugoslavia against its "greedy neighbors". A few days later Prince Paul, having realised the impossibility of following Nedić's advice, replaced him with the ageing and compliant General Petar Pešić. At the same time, Hitler, recalling Serbia's excellent military performance in the Balkan Wars and World War I, was concerned that the Yugoslav army was strong, and defeating it would necessitate the expenditure of considerable effort. Despite this, he remained concerned about the threat to the southern flank of his planned invasion of the Soviet Union posed by Greece and Yugoslavia, and aimed for a political resolution of Yugoslavia's status.
On 12 December 1940, at the initiative of the Prime Minister of Hungary, Count Pál Teleki, Hungary concluded a friendship and non-aggression treaty with Yugoslavia. Although the concept had received support from both Germany and Italy, the actual signing of the treaty did not. Germany's planned invasion of Greece would be simplified if Yugoslavia could be neutralised. Over the next few months, Prince Paul and his ministers laboured under overwhelming diplomatic pressure, a threat of an attack by the Germans from Bulgarian territory, and the unwillingness of the British to promise practical military support. Six months prior to the coup, British policy towards the government of Yugoslavia had shifted from acceptance of Yugoslav neutrality to pressuring the country for support in the war against Germany.
On 23 January 1941, William Donovan, a special emissary of US President Franklin D. Roosevelt, visited Belgrade and issued an ultimatum, saying that if Yugoslavia permitted German troop passage then the US would not "interfere on her behalf" at peace talks. Around the same time, suspicious of Prince Paul's actions, the British Prime Minister, Winston Churchill, ordered British intelligence services to establish contacts with anti-regime groups in Belgrade. On 14 February, Adolf Hitler met with Cvetković and his foreign minister and requested Yugoslavia's accession to the Tripartite Pact. He pushed for the demobilisation of the Royal Yugoslav Army—there had been a partial "reactivation" (a euphemism for mobilisation) in Macedonia and parts of Serbia, probably directed at the Italians. Hitler also pressed the Yugoslavs to permit the transportation of  German supplies through Yugoslavia's territory, along with greater economic cooperation. In exchange he
Yugoslav coup d'état