Question: On what date did negotiations take place to determine if the Soviet Union would join the Tripartite Pact?
About the article "World War II", section "Axis attack on the USSR (1941)".

Candidate passages:
After Germany entered a Tripartite Pact with Japan and Italy, Ribbentrop wrote to Stalin, inviting Molotov to Berlin for negotiations aimed to create a 'continental bloc' of Germany, Italy, Japan and the USSR that would oppose Britain and the USA.
Stalin sent Molotov to Berlin to negotiate the terms for the Soviet Union to join the Axis and potentially enjoy the spoils of the pact.
After negotiations during November 1940 on where to extend the USSR's sphere of influence, Hitler broke off talks and continued planning for the eventual attempts to invade the Soviet Union. 
After Germany entered a Tripartite Pact with Japan and Italy, in October 1940, Ribbentrop wrote to Stalin about "the historical mission of the Four Powers -- the Soviet Union, Italy, Japan and Germany -- to adopt a long range-policy and to direct the future development of their peoples into the right channels by delimitation of their interests in a worldwide scale."
Stalin replied, referencing entering an agreement regarding a "permanent basis" for their "mutual interests."
Stalin sent Molotov to Berlin to negotiate the terms for the Soviet Union to join the Axis and potentially enjoy the spoils of the pact.
Ribbentrop asked Molotov to sign another secret protocol with the statement: "The focal point of the territorial aspirations of the Soviet Union would presumably be centered south of the territory of the Soviet Union in the direction of the Indian Ocean."
Molotov took the position that he could not take a "definite stand" on this without Stalin's agreement.
In response to a written German draft four powers agreement, Stalin presented a written counterproposal, including the Soviets joining the four power Axis if Germany foreclosed acting in the Soviet's sphere of influence.
Germany never responded the counterproposal. 
Other nations involved.
Soviet Union.
Just prior to the formation of the Tripartite Pact, the Soviet Union was informed of its existence, and the potential of its joining.
Vyacheslav Molotov was thus sent to Berlin to discuss the pact and the possibility of the Soviet Union joining it.
For the Soviets, they considered joining the Tripartite Pact to be an update of existing agreements with Germany.
On Molotov's visit, he agreed in principle to the Soviet Union joining the pact so long as some details, such as Soviet annexation of Finland, could be worked out.
The Soviet government sent a revised version of the pact to Germany on November 25.
To demonstrate the benefits of partnership, the Soviet Union made large economic offerings to Germany.
Regardless of the talks however, the Germans had no intention of allowing the Soviets to join the pact.
They were already in the preparation stages for their invasion of the Soviet Union and were committed to doing so regardless of any action the Soviets took.
When they received the Soviet offer in November, they simply did not reply.
They did, however, accept the new economic offerings, and signed an agreement for such on January 10, 1941. 
Axis attack on the USSR (1941).
With the situation in Europe and Asia relatively stable, Germany, Japan, and the Soviet Union made preparations.
With the Soviets wary of mounting tensions with Germany and the Japanese planning to take advantage of the European War by seizing resource-rich European possessions in Southeast Asia, the two powers signed the Soviet–Japanese Neutrality Pact in April 1941.
By contrast, the Germans were steadily making preparations for an attack on the Soviet Union, amassing forces on the Soviet border.
Hitler believed that Britain's refusal to end the war was based on the hope that the United States and the Soviet Union would enter the war against Germany sooner or later.
He accordingly decided to try to strengthen Germany's relations with the Soviets, or failing that, to attack and eliminate them as a factor.
In November 1940 negotiations took place to determine if the Soviet Union would join the Tripartite Pact.
The Soviets showed some interest, but asked for concessions from Finland, Bulgaria, Turkey, and Japan that Germany considered unacceptable.
On 18 December 1940 Hitler issued the directive to prepare for an invasion of the Soviet Union.
On 22 June 1941, Germany, Italy and Romania invaded the Soviet Union in Operation Barbarossa, with Germany accusing the Soviets of plotting against them.
They were joined shortly by Finland and Hungary.
The primary targets of this surprise offensive were the Baltic region, Moscow and Ukraine, with the ultimate goal of ending the 1941 campaign near the Arkhangelsk-Astrakhan line, from the Caspian to the White Seas.
Hitler's objectives were to eliminate the Soviet Union as a military power, exterminate Communism, generate "Lebensraum" ("living space") by dispossessing the native population and guarantee access to the strategic resources needed to defeat Germany's remaining rivals.
Although the Red Army was preparing for strategic counter-offensives before the war, "Barbarossa" forced the Soviet supreme command to adopt a strategic defence.
During the summer, the Axis made significant gains into Soviet territory, inflicting immense losses in both personnel and materiel.
By the middle of August, however, the German Army High Command decided to suspend the offensive of a considerably depleted Army Group Centre, and to divert the 2nd Panzer Group to reinforce troops advancing towards central Ukraine and Leningrad.
The Kiev offensive was overwhelmingly successful, resulting in encirclement and elimination of four Soviet armies, and made further advance into Crimea and industrially developed Eastern Ukraine (the First Battle of Kharkov) possible.
The diversion of three quarters of the Axis troops and the majority of their air forces from France and the central Mediterranean to the Eastern Front prompted Britain to reconsider its grand strategy.
In July, the UK and the Soviet Union formed a military alliance against Germany The British and Soviets invaded Iran to secure the Persian Corridor and Iran's oil fields.
In August, the United Kingdom and the United States jointly issued the Atlantic Charter.
By October, when Axis operational objectives in Ukraine and the Baltic region were achieved, with only the sieges of Leningrad and Sevastopol continuing, a major offensive against Moscow had been renewed.
After two months of fierce battles, the German army almost reached the outer suburbs of Moscow, where the exhausted troops were forced to suspend their offensive.
Large territorial gains were made by Axis forces, but their campaign had failed to achieve its main objectives: two key cities remained in Soviet hands, the Soviet capability to resist was not broken, and the Soviet Union retained a considerable part of its military potential.
The "blitzkrieg" phase of the war in Europe had ended.
By early December, freshly mobilised reserves allowed the Soviets to achieve numerical parity with Axis troops.
This, as well as intelligence data that established a minimal number of Soviet troops in the East sufficient to prevent any attack by the Japanese Kwantung Army, allowed the Soviets to begin a massive counter-offensive that started on 5 December all along the front and pushed German troops west.
In early August, Germany and the Soviet Union worked out the last details of their economic deal, and started to discuss a political alliance.
They explained to each other the reasons for their foreign policy hostility in the 1930s, finding common ground in the anti-capitalism of both countries.
At the same time, British, French and Soviet negotiators scheduled three-party talks on military matters to occur in Moscow in August 1939, aiming to define what the agreement would specify should be the reaction of the three powers to a German attack.
The tripartite military talks, started in mid-August, hit a sticking point regarding passage of Soviet troops through Poland if Germans attacked, and the parties waited as British and French officials overseas pressured Polish officials to agree to such terms.
Polish officials refused to allow Soviet troops on to Polish territory if Germany attacked; as Polish foreign minister Józef Beck pointed out, they feared that once the Red Army entered their territories, it might never leave.
On August 19, the 1939 German–Soviet Commercial Agreement was finally signed.
On 21 August the Soviets suspended Tripartite military talks, citing other reasons.
That same day, Stalin received assurance that Germany would approve secret protocols to the proposed non-aggression pact that would place half of Poland (border along the Vistula river), Latvia, Estonia, Finland, and Bessarabia in the Soviets' sphere of influence.
That night, Stalin replied that the Soviets were willing to sign the pact, and that he would receive Ribbentrop on 23 August.