On August 25, Hitler was surprised when Britain joined a defence pact with Poland.  Hitler postponed his plans to invade Poland on 26 August to 1 September.   In accordance with the defence pact, Britain and France declared war on Germany on 3 September.  By the end of May, the projects had been officially presented.  The main tripartite negotiations began in mid-June.  Discussions focused on possible guarantees for Central and Eastern Europe in the event of German aggression.  The Soviets proposed that a political shift by the Baltic States to Germany would constitute an “indirect aggression” against the Soviet Union.  Britain rejected such proposals because they feared that the language proposed by the Soviets would justify Soviet intervention in Finland and the Baltic states, or push those countries to seek closer relations with Germany.   The debate over a definition of “indirect aggression” became one of the sticking points between the parties and, in mid-July, tripartite political negotiations were virtually heated, while the parties agreed to begin negotiations on a military agreement that the Soviets insisted could be reached at the same time as a political agreement.  On the eve of the start of the military negotiations, the Soviet Politburo pessimistically expected that the forthen negotiations would be in vain and formally decided to seriously consider the German proposals.
 Military negotiations began on 12 August in Moscow with a British delegation led by retired Admiral Sir Reginald Drax, the French delegation led by General Aimé Doumenc and the Soviet delegation led by Defence Commissioner Kliment Voroshilov and Chief of Staff Boris Shaposhnikov. In the absence of written certifications, Drax did not have the power to guarantee anything to the Soviet Union and the British government ordered it to extend the talks for as long as possible and avoid the question of whether Poland would allow Soviet troops to enter the country if the Germans invaded the country.  When negotiations failed, a great chance to prevent German aggression was probably lost.  A secret protocol was attached to this public non-aggressiveness block, which was also concluded on 23 August 1939 and divided all of Eastern Europe into spheres of German and Soviet influence. Poland to the east of the line formed by the Narnev, Vistula and San rivers would fall under the Soviet sphere of influence.