In the 1980s, the Soviet Union was embarking on political and economic reform. It began demanding payment from North Korea for past and current aid – amounts North Korea could not repay. By 1991, the Soviet Union dissolved, ending all aid and trade concessions, such as cheap oil. Without Soviet aid, the flow of imports to the North Korean agricultural sector ended, and the government proved too inflexible to respond. Energy imports fell by 75%. The economy went into a downward spiral, with imports and exports falling in tandem. Flooded coal mines required electricity to operate pumps, and the shortage of coal worsened the shortage of electricity. Agriculture reliant on electrically-powered irrigation systems, artificial fertilizers and pesticides was hit particularly hard by the economic collapse.