A shogunal succession crisis with three possible starting points
The Sengoku period grew out of the decline of the Ashikaga shogunate’s central authority, worsened by a succession dispute after the shogun Ashikaga Yoshimasa first named his brother as heir and then had a son of his own, Ashikaga Yoshihisa, a conflict that rival military families, particularly the Hosokawa and Yamana factions, exploited to expand their own power. Historians propose three separate starting points for the period: the Kyotoku incident of 1454, which triggered decades of warfare in the Kanto region; the Onin War of 1467, the traditional and most widely cited date; and the Meio incident of 1493, in which the deputy shogun Hosokawa Masamoto deposed the sitting shogun Ashikaga Yoshitane.
Chronicles of daimyo who each won only part of the story
Regional lords, or daimyo, rose and fell across the period largely through their own military and administrative success rather than through any centrally coordinated campaign, with figures such as Mori Motonari building his clan into the dominant power of western Honshu and Uesugi Kenshin fighting a prolonged rivalry against Takeda Shingen across five battles at Kawanakajima between 1553 and 1564. Because power remained genuinely fragmented among dozens of competing houses for well over a century, no single chronicle or perspective covers the period comprehensively, and historians reconstruct its overall shape from the surviving records of individual clans and campaigns, each necessarily partial to its own house’s version of events.
Firearms, peasant armies, and the low overthrowing the high
Portuguese traders introduced the matchlock arquebus to Japan in 1543, and Japanese craftsmen reproduced the weapon quickly enough that manufacturing centres had developed at Negoro, Sakai and Kunitomo within a few years, enabling larger infantry armies built around commoners equipped with firearms and spears rather than exclusively mounted, elite warriors. This shift accompanied a broader phenomenon Japanese sources called gekokujo, the low overthrowing the high, in which battlefield success could carry individuals of humble origin to real power, most strikingly Toyotomi Hideyoshi, who rose from an obscure family background to become one of the period’s supreme unifiers.
No agreed start, and no agreed end either
Just as historians disagree on the period’s start, they also propose several different end dates, 1568, 1573, 1590, 1600 or 1615, depending on which criterion is used: Oda Nobunaga’s entry into Kyoto in 1568, the final collapse of the Ashikaga shogunate in 1573, Toyotomi Hideyoshi’s defeat of the Later Hojo clan in 1590 completing territorial unification, Tokugawa Ieyasu’s decisive victory at Sekigahara in 1600, or the Siege of Osaka in 1615, which eliminated the last significant military rival to Tokugawa authority. This lack of agreement reflects a genuine underlying question about whether the period should be defined by military dominance, formal political succession, territorial unification, or the elimination of remaining rivals, since these milestones fell in different years and none obviously outweighs the others as the defining marker.
Three unifiers finishing what none of them completed alone
Unification proceeded through three successive leaders rather than any single figure: Oda Nobunaga broke the power of major rivals and religious military strongholds and entered Kyoto in 1568 before his assassination in 1582 at the hands of one of his own generals; Toyotomi Hideyoshi completed much of the remaining territorial consolidation, defeating the Later Hojo clan in 1590; and Tokugawa Ieyasu secured overall supremacy at the Battle of Sekigahara in 1600 and formally established the shogunate that would govern Japan for the next two and a half centuries in 1603, with the 1615 Siege of Osaka removing the last serious challenge to his family’s rule.
A century worth reading for its uncertainty as much as its battles
The Sengoku period is worth reading as much for what remains genuinely undecided about it, its start date, its end date, even the relative weight given to technological versus political explanations for how it unfolded, as for its sequence of famous battles and unifying leaders. Readers drawn to military history will find in the firearms-driven transformation of Japanese warfare a genuinely significant case study; readers more interested in how historians periodise complex, decentralised conflicts will find the ongoing disagreement over start and end dates a useful demonstration that even a well-documented century can resist a single tidy chronology.