He's referencing the Perry Expedition of 1852-1853, known as the Arrival of the Black Ships in Japan, during which Americans forced Japan to open up for trade at gunpoint. This led to the fall of the Shogunate and the Meiji Restoration, which launched modern Japan. The trauma of the event probably also played a significant part in Japanese consciousness during the latter part of the 19th century and early 20th century, emphasizing the importance of Japan becoming a big, strong, imperialistic power or end up colonized by the USA, which in turn directly led to the Pacific War.