Pearl Harbor was bombed by Japan on December 7, 1941, which ultimately resulted in the United States declaring war on Japan. Because of this act, Japan and the British Empire were now officially at war with one another. Japan attacked not just Pearl Harbor but also the Malay Peninsula and Hong Kong in addition to those other locations.
In both of these regions, the British maintained a sizeable military presence; yet, the Japanese were able to quickly overcome their opposition. In Singapore, the British forces capitulated only a few weeks after the initial onslaught, while in Hong Kong, they did so after only four weeks of armed conflict. This resulted in Hong Kong being ruled by the Imperial government for a period of four years.
During this time period, Japan was successful in capturing 94% of the 85,000 allies that were stationed in these two places.