Answer: Oil.
Japan wanted southern Indochina's supply of oil as they were starved for it and unable to maintain their military. On the same day they attacked Pearl Harbour they also attacked the Philippines to gain access to this oil. The attack on Pearl Harbour was to prevent any armada of US ships from retaking the Philippines, which they succeeded at doing.
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The equal-field system (Chinese: 均田制度; pinyin: Jūntián Zhìdù) or land-equalization system was a historical system of land ownership and distribution in China used from the Six Dynasties to mid-Tang dynasty. ... The system was eventually adopted by other kingdoms and its use continued through the Sui and Tang dynasties.
