Since the 1910s, Japanese planters had been involved in numerous estates and in the mining of mineral resources in Johor as a result of the Anglo-Japanese Alliance. After the First World War, rubber cultivation in Malaya was largely controlled by Japanese companies. Following the abolition of the "Rubber Lands Restrictions (Enactment)" in 1919, Gomu Nanyo Company (South Seas Rubber Co. Ltd.) began cultivating rubber in the interior of Johor. By the 1920s, Ibrahim had become a personal friend of Tokugawa Yoshichika, a scion of the Tokugawa clan whose ancestors were military leaders ("shōgun" in Japanese) who ruled Japan from the 16th to the 19th centuries. In the Second World War, at a great cost of lives in the Battle of Muar in Johor as part of the Malayan Campaign, Imperial Japanese Army (IJA) forces with their bicycle infantry and tanks advanced into Muar District (present-day Tangkak District) on 14 January 1942. During the Japanese forces' arrival, Tokugawa accompanied General Tomoyuki Yamashita's troops and was warmly received by Ibrahim when they reached Johor Bahru at the end of January 1942. Yamashita and his officers stationed themselves at the Sultan's residence, Istana Bukit Serene, and the state secretariat building, Sultan Ibrahim Building, to plan for the invasion of Singapore. Some of the Japanese officers were worried since the location of the palace left them exposed to the British, but Yamashita was confident that the British would not attack since Ibrahim was also a friend to the British, which proved to be correct.