In the decade before June 25, 1863, Japan had been living under a humiliation it could not name clearly enough to fix. In 1853 and 1854, Commodore Perry's 'Black Ships' had sailed into Japanese waters and forced the Tokugawa shogunate (とくがわしょうぐんけ) to open treaty ports to American trade. The shogunate had not wanted to comply. It had no choice. Japan lacked the naval capacity to resist, and every senior official knew it. They signed the treaties anyway and hoped the crisis would pass quietly.

It did not. The sonnō jōi (尊皇攘夷) movement — 'revere the emperor, expel the barbarians' — had been building for years among radical samurai who saw the shogunate's compliance as a betrayal of Japan's sovereignty and the emperor's authority. The four characters encoded a program: remove the foreigners, restore imperial rule, and purify Japan of outside contamination. The shogunate was an obstacle to all three goals.

In March and April of 1863, Emperor Kōmei (こうめいてんのう) took an extraordinary step. Breaking with centuries of imperial tradition of non-interference in politics, he personally issued an Order to Expel Barbarians (攘夷実行の勅命, jōi jikkō no chokurei). A deadline was set: May 10 by the lunar calendar, corresponding to approximately late June in the Gregorian calendar. The shogunate received the order and did nothing. It knew perfectly well that acting on it would mean war with powers Japan could not defeat.

The Choshu domain (長州藩, Chōshū-han), ruled by daimyo (だいみょう) Mori Takachika (もりたかちか), was the most radical sonnō jōi domain in Japan. When the deadline arrived, Choshu acted alone. On June 25, 1863, two Choshu warships — European-built vessels acquired by the domain — opened fire without warning on the American merchant steamer Pembroke, riding at anchor near the Shimonoseki Strait (しものせきかいきょう), the narrow waterway between Honshu (ほんしゅう) and Kyushu (きゅうしゅう). Captain Simon Cooper and his crew scrambled in panic. From the Choshu vessels, warriors reportedly shouted across the water: 'Sonnō jōi!' — a political slogan bellowed at an unarmed merchant ship.

There was a detail about the Choshu guns that was particularly striking: some of the Dahlgren cannons used in the attack had been presented to Japan as a gift from the United States government. Choshu fired American-donated weapons at an American vessel.

The attacks continued over the following days. On June 26, a French naval dispatch vessel was fired on by Choshu shore artillery. On July 11, the Dutch warship HNLMS Medusa entered the strait despite warnings and was struck by more than thirty shells, suffering nine killed or wounded. Choshu had turned the Shimonoseki Strait into a blockade.

American retaliation came on July 16, 1863. The USS Wyoming, under Commander David McDougal, sailed alone into the strait and engaged all three Choshu warships simultaneously. Wyoming was a single ship against three. McDougal fought anyway. When it was over, Wyoming had sunk two of the three Choshu vessels and damaged the third, inflicting approximately 40 Japanese casualties. Wyoming suffered 4 dead and 7 wounded. It was a decisive tactical defeat for Choshu — and it changed nothing about their ideology.

The definitive reckoning came in September 1864, when a multinational fleet of 17 warships representing Britain, France, the Netherlands, and the United States entered the strait, bombarded and destroyed Choshu's shore fortifications, captured 62 cannons, and put landing parties ashore. It was a comprehensive, humiliating defeat.

Takasugi Shinsaku (たかすぎしんさく), recalled as Choshu's military director after the disaster, drew the conclusion that would transform the domain and eventually Japan. He had visited Shanghai in 1862 and watched the Taiping Rebellion — an internal war tearing apart the Qing dynasty while Western powers watched and profited. He came home convinced that Japan had to modernize or be colonized. The 1864 bombardment proved his analysis with devastating force.

Takasugi's response was the Kiheitai (奇兵隊, きへいたい) — the 'militia of extraordinary soldiers.' It broke a foundational rule of samurai society: it included commoners. Farmers, merchants, townspeople — not just men of the warrior class — trained together with Western weapons and tactics. The force that would help overthrow the shogunate was built by a samurai who decided samurai alone couldn't do it. Takasugi was 23 years old at the time of the Pembroke attack. He died of tuberculosis in May 1867, at age 27 — one year before the Meiji Restoration he had helped make inevitable.

The men who fired on the Pembroke shouting 'expel the barbarians' became, within a decade, the architects of an army built on Western principles. The phrase that opened with cannon fire in the Shimonoseki Strait ended with the Meiji Restoration — and with Japan's deliberate, disciplined effort to become powerful enough that no foreign fleet could ever dictate terms again.