Introduction: A Collision Amidst a Nation in Flux

On a dark night in May 1867, a collision between two steam-powered vessels in Japan’s Seto Inland Sea became a defining moment in the country’s turbulent transition from feudal isolation to modern nationhood. The merchant ship Irōmaru, owned by the Tosa domain’s pioneering trading enterprise, was struck twice by the Kōmyōmaru, a steamer from the powerful Kii domain, and sank beneath the waves. This event, known as the Irōmaru Incident, was Japan’s first recorded collision between civilian steamships—a symbol of the nation’s rapid modernization and the growing pains that came with it.

Yet this maritime accident was no ordinary shipwreck. It unfolded against the backdrop of the chaotic Bakumatsu period, a time when the Tokugawa shogunate was losing its grip, regional domains jockeyed for power, and Japan wrestled with how to integrate Western technology and law. The incident exposed the complexities of domain rivalries, the limitations of traditional legal systems, and the visionary leadership of figures like Sakamoto Ryōma, whose advocacy for Western-style dispute resolution would leave a lasting legacy on Japan’s path to modernity.

Japan’s Bakumatsu Era and the Dawn of Steam Navigation

The mid-19th century was a time of profound upheaval in Japan. After more than two centuries of self-imposed isolation under the Tokugawa shogunate’s sakoku policy, foreign powers forced the country to open its ports to trade. This sudden influx of Western influence accelerated the adoption of new technologies, including steam-powered vessels, which revolutionized maritime transport. Steamships promised faster, more reliable voyages, crucial for a nation composed of thousands of islands.

However, Japan’s legal and political frameworks lagged behind these technological shifts. The shogunate’s feudal order, with its rigid domain system, was ill-equipped to handle disputes arising from new commercial activities and international interactions. Domains operated semi-autonomously, often competing fiercely with one another, and the old legal customs centered around hierarchical authority rather than codified, impartial laws.

In this context, the collision between the Irōmaru and Kōmyōmaru was not just a maritime accident—it became a test case for how Japan would confront the challenges of modernization and legal reform.

The Irōmaru and the Kōmyōmaru: Ships and Stakeholders

The Irōmaru was not an ordinary merchant vessel. It was leased by the Kaientai, a groundbreaking trading and shipping company founded by Sakamoto Ryōma in Nagasaki. Ryōma, a visionary samurai from Tosa domain, had previously served as the head of the Kobe Naval Training School before its closure by the shogunate. In Nagasaki, he established the Kaientai, a company that operated much like a modern corporation, engaging in arms importation and shipping to support the military modernization efforts of various domains.

Kaientai’s leasing of the Irōmaru from the Ōzu domain was a forward-thinking business arrangement. The company paid a fixed fee for each voyage, reflecting an advanced understanding of commercial operations uncommon in feudal Japan. The Irōmaru thus represented the intersection of emerging capitalist enterprise and traditional domain authority.

The collision ship, Kōmyōmaru, was owned by the Kii domain, a powerful feudal territory closely allied with the Tokugawa shogunate. The Kii domain’s influence was considerable, as it was governed by relatives of the ruling shogun, making it a formidable political player.

The Incident: Night Collision and Immediate Aftermath

On May 26, 1867, under the cover of night on the Seto Inland Sea—a vital maritime artery connecting Japan’s western and eastern provinces—the Irōmaru was proceeding on a routine voyage. Suddenly, the Kōmyōmaru appeared on the horizon. Due to the absence of a crew on watch aboard the Kōmyōmaru, the two ships collided twice in quick succession. The Irōmaru was severely damaged and sank to the sea bottom.

The immediate question was who bore responsibility for the disaster. Given the negligence aboard the Kōmyōmaru, which had no crew at the helm, the Kii domain should have been liable. However, the political reality complicated matters. The Kii domain, backed by the shogunate, insisted that the Tokugawa government adjudicate the dispute, confident that the centralized authority would favor them.

To make matters worse, the Ōzu domain demanded that the Tosa domain compensate them for losses amounting to 30,000 ryō—a considerable sum. This placed Tosa, the home domain of Sakamoto Ryōma and Kaientai, in a bind, caught between powerful neighbors and internal pressures.

Sakamoto Ryōma’s Bold Stand: Advocating International Law

Amid this tense standoff, Sakamoto Ryōma emerged with a revolutionary proposal. He recognized that Japan’s traditional feudal legal mechanisms were insufficient for resolving disputes in an era of modern commerce and international interaction. Ryōma argued that Japan would soon become a maritime nation, and similar incidents would inevitably occur. The precedent set in this first case would establish the framework for handling future maritime disputes.

Ryōma insisted that the dispute be settled according to international law, specifically the principles outlined in the “Law of Nations” , a widely recognized Western legal text. Written by American diplomat Henry Wheaton in 1836, the Law of Nations codified rules for the conduct of states and the treatment of individuals and property in international affairs. By invoking this text, Ryōma sought to transcend the parochial interests of the feudal domains and align Japan with the global community’s legal standards.

He famously declared, “If we want the world to recognize Japan, we must first abide by this law ourselves.” This appeal to universal principles was unprecedented in Japan and demonstrated Ryōma’s foresight about the country’s future on the world stage.

The Challenge of Introducing Western Law in Japan

While Ryōma’s invocation of the Law of Nations was visionary, it was not without opposition and challenges. The text had been introduced to East Asia in Chinese , partly through the efforts of reform-minded officials in the Qing dynasty, who hoped to modernize their own legal systems. Yet in China, many conservative scholars viewed the foreign legal code with suspicion, fearing it would undermine traditional Confucian order and the tributary system that defined East Asian diplomacy.

Japan’s reception was more pragmatic. The country was eager to modernize and compete with Western powers, which made the adoption of international law more palatable. Nonetheless, the Law of Nations had yet to be formally integrated into Japanese legal practice, and there was skepticism about who had the authority to enforce it domestically.

In fact, the Kii domain argued that because Japan lacked experience and institutions to execute such laws, the Law of Nations could not be applied. This highlighted a broader dilemma: Japan was in transition, embracing Western ideas while still governed by feudal structures that resisted radical reform.

Negotiations and Resolution: A Precedent for Modern Dispute Settlement

Despite the deadlock and intense debate, Ryōma’s insistence forced the Tosa and Kii domains into negotiations. Though neither side fully embraced the new legal framework, the process marked a significant step toward modern conflict resolution in Japan.

Ultimately, the dispute was settled through compromise, with the Kii domain acknowledging responsibility for the collision and assuming reparations, although the precise terms remain less documented. More importantly, the application of international legal principles, even as a reference rather than binding law, set a precedent for future maritime and commercial disputes.

The Irōmaru Incident demonstrated that Japan could not rely solely on feudal customs and domain rivalries to manage the complexities of a modernizing society. Instead, it showed the necessity of adopting universal legal norms and creating institutions capable of enforcing them.

The Legacy of the Irōmaru Incident and Sakamoto Ryōma’s Vision

The Irōmaru Incident’s significance extends beyond maritime law. It symbolizes Japan’s transformation during the late Edo period, when visionary leaders like Sakamoto Ryōma sought to reconcile tradition with modernity. Ryōma’s founding of the Kaientai as a corporate-style venture, his openness to Western ideas, and his advocacy for legal reform all embodied the spirit of change that would culminate in the Meiji Restoration of 1868.

The Meiji government would soon embark on sweeping reforms, including the establishment of a centralized legal system, the adoption of Western-style laws, and the modernization of the navy and merchant marine. The principles demonstrated in the Irōmaru case foreshadowed these developments.

Moreover, the incident underscored the importance of international law in Japan’s emergence as a global power. By engaging with Western legal norms early, Japan distinguished itself from neighboring China, which struggled to integrate such ideas, and positioned itself to negotiate on equal footing with Western nations.

Conclusion: A Maritime Accident that Charted a Course for Modern Japan

The sinking of the Irōmaru may have been a tragic accident on the surface, but its repercussions rippled through Japanese society and governance. It exposed the challenges of adapting feudal institutions to a rapidly changing world and highlighted the need for legal modernization grounded in international standards.

Thanks to the bold leadership of Sakamoto Ryōma and the willingness of some domains to engage in dialogue, the Irōmaru Incident became more than a shipwreck; it became a catalyst for Japan’s legal and political transformation. In embracing the Law of Nations as a guiding principle, Japan took a decisive step toward becoming the maritime and industrial power it is today.

This episode serves as a reminder that progress often arises from crisis, and that visionary individuals can steer the course of history by daring to challenge the status quo.