<P> From 1923, defence of British colonies and protectorates in East Asia and Southeast Asia was centred on the "Singapore strategy". This made the assumption that Britain could send a fleet to its naval base in Singapore within two or three days of a Japanese attack, while relying on France to provide assistance in Asia via its colony in Indochina and, in the event of war with Italy, to help defend British territories in the Mediterranean . Pre-war planners did not anticipate the fall of France: Nazi occupation, the loss of control over the Channel, and the employment of French Atlantic ports as forward bases for U-boats directly threatened Britain itself, forcing a significant reassessment of naval defence priorities . </P> <P> During the 1930s, a triple threat emerged for the British Commonwealth in the form of right - wing, militaristic governments in Germany, Italy and Japan . Germany threatened Britain itself, while Italy and Japan's imperial ambitions looked set to clash with the British imperial presence in the Mediterranean and East Asia respectively . However, there were differences of opinion within the UK and the Dominions as to which posed the most serious threat, and whether any attack would come from more than one power at the same time . </P> <P> On 1 September 1939, Germany invaded Poland . Two days later, on 3 September, after a British ultimatum to Germany to cease military operations was ignored, Britain and France declared war on Germany . Britain's declaration of war automatically committed India, the Crown colonies, and the protectorates, but the 1931 Statute of Westminster had granted autonomy to the Dominions so each decided their course separately . </P> <P> Australian Prime Minister Robert Menzies immediately joined the British declaration on 3 September, believing that it applied to all subjects of the Empire and Commonwealth . New Zealand followed suit simultaneously, at 9.30 pm on 3 September (local time), after Peter Fraser consulted the Cabinet; although as Chamberlain's broadcast was drowned by static, the Cabinet (led by Fraser as Prime Minister Mickey Savage was terminally ill) delayed until the Admiralty announced to the fleet a state of war, then backdated the declaration to 9.30 pm . South Africa took three days to make its decision (on 6 September), as the Prime Minister General J.B.M. Hertzog favoured neutrality but was defeated by the pro-war vote in the Union Parliament, led by General Jan Smuts, who then replaced Hertzog . Canadian Prime Minister Mackenzie King declared support for Britain on the day of the British declaration, but also stated that it was for Parliament to make the formal declaration, which it did so one week later on 10 September . The Irish Free State, which had been a dominion until 1937, remained neutral </P>

When did britain enter the second world war
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