On 7 December 1941, the Empire of Japan entered the war by attacking the British colony of Malaya and the American naval base at Pearl Harbor. Four days later, Germany declared war on the United States, bringing the Americans into the European conflict. The United States military favoured Operation Sledgehammer, a cross-channel invasion of German-occupied France. Such a move was opposed by the British, who acknowledged the military weakness of the Allies to undertake such an endeavour, especially as the British Army would have to provide the main force for such an operation. In July 1942, the Anglo-Americans met in London and agreed that Operation Roundup, Sledgehammer's successor, would be postponed and joint operations would begin in North Africa.