Since Britain had signed a treaty protecting Poland why did Britain only declare war on Germany and not Russia as well since they both invaded Poland?
The Polish ambassador in London, Raczyński, contacted the British Foreign Office pointing out that clause 1(b) of the agreement which concerned an "aggression by a European power" on Poland, should apply to the Soviet invasion. The Foreign Secretary Lord Halifax responded that the obligation of British Government towards Poland arising out of the Anglo-Polish Agreement, was restricted to Germany, according to the first clause of the secret protocol.