Thousands of Estonians opposing the second Soviet occupation joined a guerrilla movement known as the "Forest Brothers". The armed resistance was heaviest in the first few years after the war, but Soviet authorities gradually wore it down through attrition, and resistance effectively ceased to exist in the mid-1950s. The Soviets initiated a policy of collectivisation, but as peasants remained opposed to it a campaign of terror was unleashed. In March 1949 about 20,000 Estonians were deported to Siberia. Collectivization was fully completed soon afterwards.