Background
The Battle of Tongguan in the sixteenth year of Jian'an (211) was the pivotal campaign in which Cao Cao, after his setback at Chibi, shifted his strategic weight to the northwest. Ma Chao and Han Sui led a ten-part coalition from the Guanzhong region — claimed at one hundred thousand strong — to take position at Tongguan. Cao Cao mobilized his central army and marched north, and the two sides entered a prolonged standoff straddling the Wei River. When the campaign settled into a stalemate, Cao Cao recognized that a frontal assault offered little chance of success, and adopted Jia Xu's estrangement stratagem — a technique classical since the Western Han, but one that Jia Xu executed with extraordinary elegance. In chapters 58 and 59 of the novel Romance of the San Guo, this process of estrangement is broken into multiple dramatic layers, each precisely aimed at the structural rift between Ma and Han: Han Sui had been a sworn blood-brother of Ma Teng, Ma Chao's late father, and stood in the generational position of an uncle to Ma Chao; yet the two each commanded their own troops and their own contingents — an alliance in name that was in reality a partnership.
Key Figures
Jia Xu, courtesy name Wenhe, was a native of Wuwei in Liangzhou who had successively served Dong Zhuo, Li Jue, Zhang Xiu, and Cao Cao, and was famous as "a master of survival in a chaotic age." His "estrangement of Ma and Han" in the novel stands as one of his most celebrated stratagems. Cao Cao in this campaign was at once the employer and the performing actor: Jia Xu conceived the plan, Cao Cao executed it — a pairing that the novel holds up as a model of "lord and minister in tactical concert." Ma Chao, courtesy name Mengqi, was the supreme warrior of the western frontier, peerless in valor on the battlefield but relatively weak in political judgment — the fundamental premise on which the estrangement plan could succeed. The novel establishes early in chapter 58 that "Han Sui received Cao Cao's letter urging surrender; Ma Chao flew into a rage and went to Han Sui's camp to demand an explanation", showing that the distrust between Ma and Han was not conjured up by Jia Xu from thin air but was an existing crack that Jia Xu merely enlarged and ignited at the right moment. Han Sui, the veteran Liangzhou commander, genuinely wished to maintain cooperation with Ma Teng's family, but he was aging, cautious by temperament, and inclined toward negotiated settlement under the pressure of Cao Cao's superior forces — precisely the quality that became the tinder for Ma Chao's suspicion that he was "seeking a separate peace."
Core Issues
The core of Jia Xu's estrangement plan was exploiting information asymmetry to sow mutual suspicion. The entire operation was carefully designed in three steps. The first step was the "single-rider parley": Cao Cao rode out alone to exchange a long conversation with Han Sui in front of the armies. No one knew what was said — the deliberate air of mystery made Ma Chao suspicious. The second step was the "altered letter": Cao Cao wrote personally to Han Sui and deliberately struck through and defaced the critical passages himself, so that when Ma Chao saw the letter he would assume Han Sui had made the changes to conceal his secret dealings with Cao Cao. The third step was "quietly reaching the generals": Jia Xu simultaneously contacted Yang Qiu, Hou Xuan, Li Kan, Ma Wan, Liang Xing, and other officers under Han Sui's command, prompting them to drop hints in front of Ma Chao that "matters should not be delayed". With all three layers stacked, the "evidence" that Ma Chao received multiplied from one item to three. Even if he knew rationally that his uncle-figure would not betray him, emotionally he could no longer suppress his suspicions. This technique of "fabricating multiple items of false evidence all pointing to the same conclusion" has been regarded to this day in the history of intelligence operations as one of the paradigmatic forms of the estrangement stratagem.
Political Consequences
The climax of the episode was Ma Chao's storming of Han Sui's tent — he saw with his own eyes that the five generals were in private conversation with Han Sui, heard Yang Qiu say "matters should not be delayed," and immediately drew his sword and slashed; Han Sui's left hand was severed, and the five generals scattered and fled for their lives. Though Han Sui ultimately survived, the command core of the Xiliangjun coalition was shattered: the figure capable of mediating between the Ma and Han factions was gone, and Cao Cao seized the moment to launch an all-out assault the following day, routing the Guanzhong commanders one by one. From the perspective of political consequence, the true power of this estrangement plan far exceeded the battlefield outcome itself: it compressed what might have been a months-long siege into a single decisive assault, allowing Cao Cao to complete the pacification of Guanzhong within 211 and free his hand to address Liangzhou and Hanzhong. From that point on Ma Chao became a fugitive in Hanzhong before eventually joining Liu Bei's forces, Han Sui faded into old age and death, the entire western frontier military-political establishment collapsed, and Caowei's actual rule over the Guanlong region was permanently established.
Counterfactual
If Ma Chao's trust in Han Sui had been more solid, several layers of the estrangement plan might not have taken hold. The first fork: if Ma Chao, on first receiving Cao Cao's letter of inducement, had simply beheaded the messenger as a gesture of loyalty (in the novel he originally declared his willingness to live and die with Han Sui), Jia Xu would have had no opening to introduce the altered letter at all. The second fork: if Han Sui had refused to attend the single-rider parley and insisted on open discussion instead, Cao Cao's "mysterious conversation" would have lacked the material to generate suspicion. The third fork: if the Xiliangjun coalition had possessed a strategist of Zhang Liang's caliber capable of seeing through Jia Xu's design, the three layers of false evidence would have been exposed in front of Ma Chao and might actually have given Ma and Han a common grievance to unite them. But none of these forks could have happened — the structural weakness of the western frontier military establishment (multiple commanders, no unified strategist) made it inherently unable to withstand estrangement at Jia Xu's level of craft. This estrangement plan was therefore not only a triumph of individual ingenuity but a structurally inevitable outcome: a tribal-style coalition lacking a unified strategist will always fall before a centralized army that possesses one.