The first recorded expedition arrived at the scene more than a decade after the event. In 1921, the Russian mineralogist Leonid Kulik, visiting the Podkamennaya Tunguska River basin as part of a survey for the Soviet Academy of Sciences, deduced from local accounts that the explosion had been caused by a giant meteorite impact. He persuaded the Soviet government to fund an expedition to the Tunguska region, based on the prospect of meteoric iron that could be salvaged to aid Soviet industry. Kulik's party reached the site in 1927. To their surprise, no crater was to be found. There was instead a region of scorched trees about across. A few near ground zero were still strangely standing upright, their branches and bark stripped off. Those farther away had been knocked down in a direction away from the center. By the time of the revolution Siberia was an agricultural region of Russia, with weak entrepreneur and industrial classes. The intelligentsia had vague political ideas. Only 13% of the region's population lived in the cities and possessed some political knowledge. The lack of strong social differences and scarcity of urban population and intellectuals led to the uniting of formally different political parties under ideas of regionalism. The anti-Bolshevik forces failed to offer a united resistance. While Kolchak fought against the Bolsheviks intending to eliminate them in the capital of the Empire, the local Socialist-Revolutionaries and Mensheviks tried to sign a peace treaty with the Bolsheviks, on terms of independence. Foreign allies, though being able to make a decisive effort, preferred to stay neutral, although Kolchak himself rejected the offer of help from Japan. After a series of defeats in Central Russia, Kolchak's forces retreated to Siberia. Amid resistance of Socialist-Revolutionaries and waning support from the allies, the Whites had to evacuate from Omsk to Irkutsk, and finally Kolchak resigned under pressure of the Socialist-Revolutionaries, who soon submitted to the Bolsheviks. By the 1920s the agriculture in Siberia was in decline. With the large number of immigrants, land was used very intensively, which led to exhaustion of the land and frequent bad harvests. Agriculture wasn't destroyed by the civil war, but the disorganization of the exports destroyed the food industry and reduced the peasants' incomes. Furthermore, prodrazvyorstka and then the natural food tax contributed to growing discontent. In 1920–1924 there was a number of anti-communistic riots in rural areas, with up to 40,000 people involved.