1383–1385 Portuguese Interregnum and Battle of Aljubarrota vs Jingnan Campaign

Under Pereira's leadership, the Portuguese command applied a flexible doctrine that shifted rapidly from static defense to maneuver warfare. Castile, however, persisted with the traditional feudal cavalry charge doctrine and could not adapt to changing conditions.

Zhu Di demonstrated flexible doctrine by moving between offensive, siege, and guerrilla tactics as needed. Imperial forces relied on static defense and could not adapt to changing conditions.

Attrition War — Both sides employed a combination of guerrilla attacks, sieges, and pitched battles to break the enemy's will. In particular, Pereira's constant harassment of Castilian supply lines and disease eventually eroded Castile's logistical superiority.

Siege/Challenge — The civil war was characterized by the capture of strategic cities and pitched battles. Zhu Di forced the enemy into attrition and maneuvers, compelling their surrender; Imperial forces focused on defending the capital.

Pereira targeted the main strength of the Castilian army, the heavy cavalry, by drawing it into a narrow and impassable terrain and destroying it with English archers. Castile, however, failed to correctly identify the center of gravity; relying on numerical superiority, they spread across the entire front and lost their strike force in Pereira's trap.

Zhu Di concentrated his forces against enemy command centers and logistics bases, paralyzing central authority. Imperial forces dispersed their strength trying to halt the enemy's advance on the capital, failing to create an effective center of gravity.

Pereira set a trap at Aljubarrota using the terrain's natural obstacles; Castilian reconnaissance failed to detect these preparations. Additionally, during the Siege of Lisbon, a small Portuguese fleet managed a raid that deceived the Castilian blockade and successfully delivered supplies.

Zhu Di deceived the enemy through concealment of intent, espionage, and propaganda; he even achieved diplomatic successes such as the release of Jianwen's sons. Imperial forces were defenseless against these stratagems and failed to identify Zhu Di's actual objectives.

At Aljubarrota, the English longbowmen's volleys from 200 meters broke the Castilian heavy cavalry before contact, causing panic among the French knights. Pereira's pre-prepared pits and obstacles reinforced this shock effect.

Zhu Di used firearms and Mongol cavalry in a synchronized manner to create shock effects on enemy lines. Cavalry charges, in particular, caused the Imperial infantry to disperse.

The summer heat and drought exhausted the heavily armored Castilian troops at Aljubarrota, leaving them tired and thirsty. Pereira selected a narrow valley enclosed by marshland and streams, completely nullifying Castile's numerical superiority. Additionally, the plague outbreak forced the Castilian army to abandon the Siege of Lisbon.

The cold northern climate and steppe terrain favored Zhu Di's cavalry-heavy army, while the Imperial forces' south-to-north campaigns strained their supply lines. Zhu Di gained geographic superiority by capturing key passes and fortified positions.

The Portuguese resistance, thanks to an intelligence network provided by the locals, was aware of every move of the Castilian army. In contrast, Castile misjudged the real strength of the resistance by relying on exaggerated reports from its supporters within Portugal. Especially before Aljubarrota, Castile had insufficient intelligence on Pereira's positioning.

Zhu Di accurately assessed both his own capabilities and the enemy's weaknesses. Thanks to spies at court, he was informed of Imperial plans and exploited their indecision. In contrast, Jianwen's side underestimated Zhu Di's military capacity and became vulnerable to strategic surprises due to intelligence failures.

Pereira used his interior lines advantage to rapidly shift his forces from north to south, catching Castile unprepared each time. In contrast, the Castilian army moved slowly due to heavy equipment and a disjointed command structure, and was drawn into the battlefield chosen by Pereira.

Zhu Di exploited interior lines to rapidly redeploy his troops and defeat enemy forces individually. Imperial forces moved slowly on exterior lines, losing the initiative and failing to coordinate between units.

The Portuguese independence supporters had high morale from fighting an existential struggle, reflected in Lisbon's resistance to the siege and the determined defense at Aljubarrota. On the Castilian side, fighting outside their homeland led to low motivation and increased desertions due to disease.

Zhu Di's charismatic leadership and care for his soldiers kept morale high. Conversely, frequent general changes and defeats led to a collapse of morale among Imperial forces; many units joined Zhu Di without a fight.

The Avis side, through John I's diplomatic initiatives, secured military and political support from England, gaining a strategic advantage without fighting. Additionally, by winning the support of Lisbon's populace and merchant class, they thwarted Castile's plan to be crowned in the capital and weakened Castile's legitimacy claim.

Before the war, Zhu Di exploited the mistakes of Jianwen's advisors to secure the release of his sons and neutralized opposition through spies at court. By framing his rebellion as self-defense, he gained the surrender of some provinces without a fight.