Short answers, pulled from the story.
Japanese leaders launched the Malayan campaign after embargoes from the United States, the United Kingdom, and the Netherlands cut off oil imports between 1940 and 1941. These restrictions forced Tokyo to attack American, British, and Dutch territories in South East Asia instead of withdrawing from China.
Commonwealth troops possessed only 23 obsolete Mk VIB light tanks within the 100th Light Tank Squadron of the Indian Army while Japanese forces entered Malaya with over 200 tanks including Type 95 Ha-Go light tanks and Type 97 Chi-Ha medium tanks. These vehicles lacked sufficient armament for armored warfare against the superior Japanese numbers.
Mitsubishi Ki-21 Sally bombers attacked airfields at Alor Star, Sungai Petani, and Butterworth on the 8th of December 1941. Sixty Allied aircraft were lost on the ground during this initial assault before the Japanese Navy established naval supremacy by the 10th of December.
The Battle of Slim River saw two Indian brigades practically annihilated during a risky night attack using surprise tactics while the battle near Muar River destroyed Brigadier H. C. Duncan's 45th Indian Brigade. The Parit Sulong Massacre occurred when wounded soldiers left behind were tortured and killed leaving only two survivors from one hundred thirty-five men.
The last organized Allied forces left Malaya crossing the Johore Strait toward Singapore Island on the 31st of January 1942. Engineers blew a wide hole in the causeway linking Johore and Singapore though stragglers waded across days later.