Scullin in 1929, two events occurred that substantially affected the armed forces: conscription was abolished and the economic effects of the Great Depression started to be felt in Australia. The economic ramifications of the depression led to decisions that decreased defence expenditure and manpower for the army. Since conscription was repealed, to reflect the new volunteer nature of the Citizens Forces, the CMF was renamed to the Militia. World War II Following the declaration of war on Nazi Germany and her allies by the United Kingdom, and the subsequent confirmation by Prime Minister Robert Menzies on 3 September 1939, the Australian Army raised the Second Australian Imperial Force, a 20,000-strong volunteer expeditionary force, which initially consisted of the 6th Division; later increased to include the 7th and 9th Divisions, alongside the 8th Division which was sent to Singapore. In October 1939, compulsory military training recommenced for unmarried men aged 21, who had to complete three months of training. The 2nd AIF commenced its first operations in North Africa with Operation Compass, that began with the Battle of Bardia. This was followed by supplying Australian units to defend against the Axis in the Battle of Greece. After the evacuation of Greece, Australian troops took part in the Battle of Crete which, though more successful, still failed and another withdrawal was ordered. During the Greek Campaign, the Allies were pushed back to Egypt and the Siege of Tobruk began. Tobruk's primary defence personnel were Australians of the 9th Division; the so-called 'Rats of Tobruk'. Additionally, the AIF participated in the Syria–Lebanon campaign. The 9th Division fought in the First and Second Battle of El Alamein before also being shipped home to fight the Japanese. Pacific In December 1941, following the Bombing of Pearl Harbour, Australia declared war on Japan. The pace of Japan's subsequent conquest of Southeast Asia extremely concerned Australian policymakers. Consequently, the AIF was requested to return home, and the militia was mobilised. After the Fall of Singapore, and the consequent capture of the entire 8th Division as POWs, this concern only grew. These events hastened the relief of the Rats of Tobruk, while the other divisions were immediately recalled to reinforce New Guinea. General conscription was reintroduced, though service was again limited to Australian possessions; this earned the militia their epithet of "koalas". Tensions primarily arose between the AIF and Militia due to the CMF's perceived inferior fighting ability,