[1] After the defeat of the Infantes of Aragon in the Castilian-Aragonese War of 1429-1430, the position of the Constable Álvaro de Luna at the Castilian court was consolidated, but after a few years a faction of the nobility began to oppose the almost absolute power that he had achieved thanks to King John II's trust in him.

In February 1439, he and Castilian Admiral Fadrique Enriquez signed a letter to King John II demanding the banishment of Constable Alvaro de Luna's court "with all his relatives and people, so that Your Grace may remain in all of your free power."

However, Henry soon joined the side of the revolted nobles when they promised him the return of all his possessions confiscated at the end of the Castilian-Aragonese War of 1429-1430, as well as the mastery of the Order of Santiago, which he had previously held.

A skirmish occurred a few days after the unsuccessful Tordesillas meeting in Roa, where the armies of the Count of Ribadeo, belonging to Álvaro de Luna's faction, clashed with the rebel nobility who had formed a League.

However, the discussions did not come to an end, and a temporary resolution was reached in October 1439, referred to as the Castronuño agreement, that inflicted a six-month banishment from the court on Álvaro de Luna.

On January 17, 1440, the day after receiving the message, the king chose to flee the court located in Madrigal with the prince of Asturias and the noble supporters of Alvaro.

[note 1] At the same time, support for the king and the Constable was declining as cities began to switch sides and align with the League, demonstrated by the Cortes held in Valladolid in May 1440.

To cement the pact, on September 15, 1440, the wedding of the Prince of Asturias, Henry, and Doña Blanca, daughter of the King of Navarre, was celebrated in Valladolid, as stipulated in the Concord of Toledo.

But in early January 1441, King John II fled from the court in Arévalo with the Prince of Asturias to gain independence from the Infantes of Aragon and the League.

"[10]Then they reiterated the arguments already presented to the ambassadors of John II in Madrigal, with the addition of a new one: that Alvaro de Luna intended to tyrannize the Prince of Asturias and Queen Maria.

[10] It ended by saying that the signatories, the Infantes of Aragon and the noble leaders of the League:"[have] agreed to reverse and we revert to the said Constable any security and assurances... and we revoke and annul them... and we send him to challenge by our procurators as an enemy of the said lord king... and as a sower of scandals and tumults and discords.

After leaving Arevalo, they traversed the Guadarrama mountain range and attacked Maqueda and Illescas, which were under the control of the Constable and his brother, the Archbishop of Toledo.

In late April, he besieged Torrijos, where Infante Henry was staying, asking for the help of most of the troops of the league that were concentrated in Arévalo under the command of his brother, John of Navarre.

The king's endorsement of Constable Alvaro de Luna compelled the League to view John II as their adversary, directing their forces against him.

The purpose was to prevent Constable Alvaro de Luna from striking a blow against John of Navarre and regaining control of the Castilian monarchy.

Months later, after gathering support among the high Castilian nobility, the Prince of Asturias, Henry, declared war on John of Navarre by means of a manifesto published on March 29, 1444, in which he made a special appeal to the Castilian regions bordering Navarre so that all would join the fight to free King John II, expel the "foreigners" and attack the towns of the neighboring kingdom.

Remaining under Count of Castro's custody, the subject withdrew to Palencia upon being informed of King John II's escape from Portillo Castle on June 16.

Shortly thereafter, in Mojados, the queen pledged her support to the king with a promise to stand by him "against all the people of the world, even if they were of royal state and were close to him in any degree".

Finally, John retreated to the Navarre border, but did not cross it, and waited for his brother King Alfonso the Magnanimous of Aragon to intervene, as the Prince of Asturias' declaration of war violated the Concord of Toledo of 1436.

Subsequently, he proceeded to La Alcarria, passing through Madrid and San Martin de Valdeiglesias to thwart the union of John's army with that of his brother, Henry, who was approaching from the south.

[26] In an effort to prevent Constable Alvaro de Luna from regaining the significant power he held from 1430 to 1436, Prince of Asturias Henry garnered support from nobles aligned with the Infantes of Aragon.

As noted by historian Jaume Vicens Vives, the victory in Olmedo did not reinforce the Castilian monarchy but simply led to a redistribution of perks and estates, albeit with the "royal authority recovering much of its pre-eminence in the country."

Álvaro de Luna became the new master of the Order of Santiago, and additionally received the county of Alburquerque and the lordship over the towns of Trujillo, Medellín and Cuéllar.

But this historian also agrees with Jaume Vicens Vives, emphasizing that the winners of Olmedo were the most prominent nobles of Castile who, on this occasion as well as others, reaped significant rewards.

Alvarez Álvarez concludes:"The removal of the Infantes [of Aragon] from their previous permanent intervention in Castilian lands and affairs opened a new path in the traditional confrontation between nobility and monarchy, aggravated by the existence of practically two courts, that of King John II and his valide, and that of the Prince of Asturias, the future Henry IV, with their respective parties and noble factions and interests.