Abstract
Two battles occupy nearly identical positions in the national narratives of England and Japan. Bosworth Field (22 August 1485) is treated as the terminus of the Wars of the Roses and the founding moment of the Tudor century. Sekigahara (21 October 1600) is called tenka wakeme no tatakai, the battle that divided the realm, and is credited with inaugurating two and a half centuries of Tokugawa rule. Both are canonical “decisive battles.” Yet in both cases, the outcome turned less on tactical execution than on a prior question: which contingents would actually fight, and for whom. In both, large bodies of armed men stood on the field and did nothing, or did something other than what their nominal commander expected, because of arrangements negotiated in the weeks and months beforehand. This paper argues that the mechanism of decision in both battles was diplomatic and structural rather than tactical, that this mechanism recurs widely enough to constitute a category, and that military history lacks an adequate analytical apparatus for it. It proposes a framework — conditional alignment, combat participation rates, and reward-flow analysis — for studying battles whose result was purchased rather than won.
1. The Problem with Decisiveness
Edward Creasy’s Fifteen Decisive Battles of the World (1851) established a durable template: the battle as hinge, the day as cause, the field as the place where history is settled. The template survived the professionalization of the discipline because it serves narrative and pedagogical purposes well. It is also, for the two battles considered here, close to backwards.
The first difficulty is that neither battle actually decided anything by itself. Henry VII faced a Yorkist rising under Lambert Simnel that culminated at Stoke Field in June 1487, nearly two years after Bosworth, and continued to face Yorkist pretenders, most seriously Perkin Warbeck, into the later 1490s. Ieyasu did not receive the title of shogun until 1603, and the Toyotomi house was not destroyed until the Osaka winter and summer campaigns of 1614–15. In each case, the “decisive” battle required a second settlement roughly fifteen years later before the regime was secure. Decisiveness was assigned retrospectively by dynasties with an interest in dating their own legitimacy to a single clean moment.
The second difficulty is more interesting. In both battles, the winner’s tactical contribution to the outcome was modest. What determined the result was the behavior of contingents that had already been negotiated out of the fight, or into the wrong side of it, before the first arrow or arquebus ball was loosed.
2. Bosworth: The Withheld Third
The conventional account gives Richard III a numerical advantage — figures are unreliable, but something like eight to ten thousand against Henry Tudor’s five thousand, a force heavily reliant on French and Scottish mercenaries and on Welsh levies gathered during the march from Milford Haven. Those numbers, however, exclude the decisive variable: the roughly three to six thousand men under Thomas, Lord Stanley, and his brother Sir William Stanley, positioned apart from both armies and committed to neither.
The Stanley position was not an accident of deployment. It was the visible expression of a negotiation that had been running for months. Thomas Stanley was married to Margaret Beaufort, Henry Tudor’s mother; he was thus the claimant’s stepfather while holding office under Richard. Richard understood the exposure well enough to take Stanley’s son, Lord Strange, as a hostage — a control mechanism that failed precisely because it was the only one available. Hostage-taking is the instrument of a sovereign who cannot command.
The battle itself was short, likely under two hours. Norfolk’s vanguard engaged Oxford’s and was broken; Norfolk was killed. Henry Percy, fourth Earl of Northumberland, commanding a substantial portion of Richard’s array, did not engage at all — whether from obstructed ground, calculated abstention, or the collapse of the king’s control over his own line, the sources do not permit certainty. Richard, seeing Henry Tudor’s personal standard relatively unprotected, launched a mounted charge at the claimant directly, cut down Henry’s standard-bearer William Brandon, and came within yards of ending the campaign in a stroke. Sir William Stanley then committed, struck Richard’s charge in the flank, and killed the king. Recent archaeological work relocating the engagement to the ground near Fenn Lane Farm, on the basis of an unusually dense scatter of round shot and the recovery of a silver-gilt boar badge, has firmed up the topography without altering this sequence.
What decided Bosworth, then, was a decision taken by a third party during the battle on the basis of terms arranged before it. Richard lost because roughly a third of the armed men present were either bought, neutralized, or unwilling, and because his own tactical initiative — the charge — was in fact a gamble taken by a commander who had correctly perceived that he could not win a sustained engagement with an army he did not control.
The reward flow confirms the reading. Thomas Stanley received the earldom of Derby. Sir William became Lord Chamberlain of the Household and one of the wealthiest men in England. The irony is instructive: in 1495 Sir William Stanley was executed for implication in the Warbeck conspiracy. The man who made the king by conditional loyalty was destroyed by the same logic.
3. Sekigahara: The Idle Majority
Sekigahara presents the same structure at larger scale and with far better documentation.
Ishida Mitsunari’s Western Army held, on paper, an excellent position: roughly eighty thousand men occupying high ground on three sides of a valley into which the Eastern Army had marched. Contemporary and later commentators, including Western observers of the terrain in the Meiji period, have remarked that on a map the Western deployment looks like a textbook envelopment. It failed because a large fraction of that eighty thousand had already been detached from the Western cause by correspondence.
Ieyasu’s pre-battle campaign was, in a real sense, the battle. In the months preceding the engagement he wrote a very large volume of letters — the figures cited in the literature run from well over a hundred to nearly two hundred — to daimyo across the archipelago, offering confirmations of holdings, promises of enlargement, and reassurances of standing. Kuroda Nagamasa served as the principal broker in the most consequential of these approaches.
Three results of that campaign are decisive:
Kobayakawa Hideaki, holding some fifteen thousand men on Mount Matsuo, had been in contact with the Eastern side beforehand. He remained stationary for hours while Ōtani Yoshitsugu, Ukita Hideie, and Shimazu Yoshihiro’s contingents bore the fighting, then descended against Ōtani’s flank. Ōtani, who had anticipated the possibility and prepared his line to receive it, held briefly and then collapsed; he took his own life. Additional contingents — Wakisaka Yasuharu, Ogawa Suketada, Kutsuki Mototsuna, Akaza Naoyasu — turned with or immediately after Kobayakawa. The well-known story that Ieyasu ordered arquebuses fired at Mount Matsuo to force the issue is probably a later dramatic elaboration and should be handled as such; the underlying prior arrangement is not in doubt.
Kikkawa Hiroie, in command of the Mōri vanguard positioned on Nangū Mountain, had negotiated separately with the Eastern side through Kuroda Nagamasa and simply refused to advance, physically blocking the road and preventing Mōri Hidemoto’s fifteen thousand or so from entering the battle. The traditional anecdote has him deflecting repeated requests to move with the excuse that his men were eating. Behind him, Chōsokabe Morichika and Natsuka Masaie likewise never engaged.
Mōri Terumoto, nominal commander-in-chief of the Western Army, was not present at all. He remained at Osaka Castle with the Toyotomi heir, which meant the coalition fought under a placeholder — a structural weakness that made every constituent daimyo’s participation a personal calculation rather than an obligation.
The battle lasted perhaps six hours and was over. Shimazu Yoshihiro, having barely fought, executed his famous withdrawal directly through the Eastern lines. It is worth adding that Ieyasu’s own main army, under his son Hidetada, never arrived — it was delayed besieging Sanada Masayuki at Ueda. The victor won the realm without his principal field force, which is a fair index of how little the outcome depended on his tactical weight.
Again, reward flow is the clearest evidence of what was purchased. Kobayakawa received Bizen and Mimasaka at over half a million koku. The Mōri, whose contingents never fought, were nonetheless reduced from holdings above a million koku to Suō and Nagato at roughly three hundred seventy thousand — Kikkawa’s negotiated personal exemption having been converted, at his own request, into the survival of the main house rather than his own advancement. The redistribution of some six million koku of confiscated land following Sekigahara is the settlement of accounts opened in the correspondence of the preceding summer.
4. The Shared Structure
Set side by side, the two cases share a set of features specific enough to be diagnostic.
A weak or absent center of legitimacy. Richard III’s title rested on the disputed illegitimacy of his nephews and was under active challenge. Mitsunari fought in the name of a child, Toyotomi Hideyori, whose interests could plausibly be claimed by either side — indeed Ieyasu maintained throughout that he was acting for the Toyotomi. Where legitimacy is contestable, loyalty becomes a forecast rather than a duty.
Contract-based rather than institutional mobilization. Both armies were aggregations of retinues raised by magnates who brought their own men, commanded them personally, and retained the practical capacity to withdraw them. Neither king nor regent commanded soldiers; each commanded commanders. This is the enabling condition. A force paid, drilled, and administered by the state cannot defect by contingent, because the contingent has no independent principal.
A brokered market operating before the battle. Both winners ran an explicit purchasing operation: Henry Tudor’s family channel to the Stanleys and his negotiations during the Welsh march; Ieyasu’s letter campaign through Kuroda Nagamasa. The goods sold were lands, titles, offices, and confirmations, deliverable only on victory — which is why the contracts were self-executing at the moment the outcome became legible.
Physical positions that preserved optionality. The Stanleys took ground apart from both armies. Kobayakawa held a hill on a flank; Kikkawa held a road. These are not accidents of deployment but the topography of hedging. A commander who intends to decide late positions himself where late decision remains possible — and that positioning is observable in advance.
Inadequate control instruments. Richard’s seizure of Lord Strange, Mitsunari’s reliance on hostage families held at Osaka: both are the coercive substitutes of principals who lack command. Both failed.
A large fraction of mustered strength that never fought. This is the measurable common denominator. At Bosworth, plausibly a quarter to a third of men present never engaged or engaged against their nominal side. At Sekigahara, a comparable or larger share of the Western Army stood idle.
5. Why the Field Neglects This
The neglect is not accidental; it follows from several reinforcing pressures.
Evidentiary asymmetry by design. Arrangements of this kind are made to be deniable. Oaths are sworn orally, letters are burned, brokers are used precisely so that principals can disclaim. What survives is the day’s fighting, which is public. The historian’s sources over-represent the visible half of the causal chain.
Disciplinary partition. Diplomatic history and military history are separately staffed, separately journaled, and separately trained. A phenomenon that sits exactly on the seam — diplomacy whose object is a battlefield and whose currency is manpower — falls to neither. Operational historians treat the pre-battle negotiation as background; diplomatic historians treat the battle as an outcome rather than an instrument.
Narrative convention. The battle-piece as a genre demands a decision produced on the field. The “face of battle” turn following Keegan usefully redirected attention from the general’s map to the ranker’s experience, but it moved further into the day, not backward from it. Neither the older operational tradition nor its experiential successor is built to analyze non-participation, which has no maneuver and no experience worth narrating.
Dynastic and national interest in clean founding moments. Tudor historiography, from Polydore Vergil through Hall to Shakespeare, had every reason to present Bosworth as providential judgment rather than as a purchase. Tokugawa-era accounts had a parallel interest in Sekigahara as the manifest verdict of heaven. Both traditions preferred treachery to be a moral coloring on someone else’s character rather than the operative causal mechanism of the winner’s success.
The absence of a metric. There is no standard figure in the literature for the proportion of a mustered army that actually engaged. Orders of battle report presence, not participation. Without a number, the phenomenon cannot be compared across cases, and what cannot be compared does not become a field.
6. Objections and Limits
The argument can be overstated in three ways, and honesty requires naming them.
Defection was itself conditional on the fighting. Kobayakawa did not descend at dawn; he descended after hours of engagement had made the Western Army’s exhaustion legible. Sir William Stanley committed at the moment Richard’s charge had separated the king from his main body. The prior arrangement set the terms; the fighting set the price and the timing. The correct formulation is not that tactics were irrelevant but that tactics functioned as a signal-generating process for a decision made on other grounds. A more careful thesis: the battle determined when the pre-arranged outcome would be executed, not what it would be.
The sources are interested. The Ballad of Bosworth Field, a principal narrative source for Stanley conduct, is a Stanley family production and inflates their role accordingly. Japanese accounts of Sekigahara accumulated dramatic material across the Edo period, and the arquebus story is a good example of an episode that reads as retrospective. A research program built on this thesis must be built on documents contemporary with the negotiation — letters, oath texts, land grants — rather than on battle narratives written afterward by the beneficiaries.
Selection risk. Choosing two battles because they exhibit the pattern proves nothing about frequency. The framework requires negative cases. Barnet in 1471 is a useful control: its confusion arose from fog and misidentified badges rather than from purchased defection, and it produced a clear result through fighting. Towton likewise. The question worth answering is not whether defection sometimes decides battles but under what structural conditions it does, which requires counting both outcomes.
7. A Research Agenda
Four concrete lines would move this from an observation to a field.
A combat participation rate. For any battle with adequate order-of-battle data, compute the proportion of mustered manpower on each side that made contact. Publishing this figure alongside conventional strength estimates would surface the phenomenon immediately across hundreds of engagements and make comparison possible.
A typology of alignment. Contingents should be classified before the battle, not after: fully committed; conditionally committed (will fight if the side is winning); contracted-neutral (paid to abstain); contracted-defector (paid to switch). The four categories carry different evidentiary signatures and different topographic behavior.
Reward-flow analysis as revealed preference. Post-battle land redistribution, attainders, grants, and offices are the audit trail of pre-battle contracts. The Sekigahara redistribution and the Tudor attainder and grant records of 1485–86 are unusually rich and directly comparable. Where the correspondence was destroyed, the payments survive.
Comparative extension. The pattern is not confined to these two cases. Marj Dabiq in 1516, where Khair Bey’s defection collapsed the Mamluk left against the Ottomans, is a close analogue. Shizugatake in 1583 turned substantially on Maeda Toshiie’s withdrawal from Shibata Katsuie’s line. Plassey in 1757 is the canonical instance of a battle whose result was contracted in advance, with Mir Jafar’s inert contingents making the numerical disparity meaningless. A comparative volume drawing on these plus the two treated here would establish the category across regions and centuries and rule out the objection that it is a peculiarity of late-medieval European or Sengoku Japanese practice.
8. Conclusion
Bosworth and Sekigahara are taught as the days on which two nations changed. They are better understood as the days on which a set of prior agreements was executed. In both, the losing commander brought more men to the field than his opponent and lost because he did not control them; in both, the winner had spent the preceding months converting his enemy’s order of battle into a ledger of obligations payable on victory. The fighting was real, and it mattered — it established which arrangements would be honored and when — but it was not the mechanism of decision.
The historiographical cost of missing this is not merely that two battles are misdescribed. It is that a general phenomenon in premodern and early modern warfare — the conversion of diplomatic capital into battlefield manpower, and the resulting fragility of coalition armies raised on contract rather than command — has no name, no metric, and no literature. That gap is worth closing, and the two most famous decisive battles in English and Japanese history are the right place to begin.
