Economic tension intensified during the Second World War. The Japanese occupation of Malaya began in 1941 and from that point onwards the "export of primary products was limited to the relatively small amounts required for the Japanese economy." This led to large areas of rubber plantations being abandoned and many mines closing. Mining was also affected by a shortage of spare parts for machines. Imports of rice, which made up a large portion of the Malayan diet, fell rapidly due to limited trade and thus the population was forced to focus their efforts on subsistence.