In 1939, after Soviet efforts to contain Nazi aggression through co-operation and alliance with France and Britain were rejected by the French and British, Nazi Germany and the Soviet Union signed a Non-Aggression Treaty. despite ideological opposition between the countries, the USSR agreed not to engage in hostilities against Germany at the outbreak of World War II (Australia declared war on Nazi Germany for invading Poland). Consequently, the Communist Party of Australia opposed and sought to disrupt Australia's war effort against Germany in the early stages of the War under orders of the Communist International on the grounds that it was a war between Imperialist nations, and not in the interests of the working class. Menzies banned the CPA after the fall of France in 1940, but by 1941 Stalin was forced to join the allied cause when Hitler reneged on the Pact and invaded the USSR. The USSR came to bear the brunt of the carnage of Hitler's war machine and the Communist Party in Australia lost its early war stigma as a result. Its membership rose to 20,000, it won control of a number of important trade unions, and a Communist candidate, Fred Paterson, was elected to the Queensland parliament. But the party remained marginal to the Australian political mainstream. The Australian Labor Party remained the dominant party of the Australian working class.