The Spanish conquest of the Iberian part of Navarre was initiated by Ferdinand II of Aragon and completed by his grandson and successor Charles V in a series of military campaigns lasting from 1512 to 1524.

For its part, King Ferdinand II looked among the magnates of Navarre for allies, finding it in Louis of Beaumont, Count of Lerin, who demanded to rule over Los Arcos and Laguardia.

Finally, an arrangement with Alain of Albret paved the road for the young Gascon noble John's accession to the throne of Navarre in February 1484, thwarting again the Aragonese king's plans.

In March that year, Alain signed the Treaties of Valencia with Ferdinand, including military agreements for the defense of Navarre against France, and recognition of Bearn as sovereign.

The monarchs Catherine and John opted to support Philip after the expulsion of Ferdinand II from Castilian politics in July 1506, resulting in the Treaty of Tudela de Duero.

When the Courts of Navarre (The Three States) and the States-General of Béarn were confronted with the possibility of a French takeover in 1510, a military mobilization was decreed and a bill passed to create a Béarn-Navarre confederation and a permanent joint defense provision against external assault.

At the same time a Navarrese diplomatic mission sent to France was holding talks with Louis XII lasting a month, while Ferdinand threatened to cross the border if an agreement was reached.

[3]: 23, 88–91  The next day Ferdinand sent his troops across the border from Álava into Navarre, commanded by General Don Fadrique de Toledo, Duke of Alba, who had been involved in the conquest of Granada.

Tudela in turn was besieged, and resisted the Aragonese assault led by Alfonso of Aragon, a bastard son of Ferdinand II and archbishop of Zaragoza, who was commanding 3,000 infantry and 300 cavalry.

[5]: 29  The determined loyalty of the local authorities to the Navarrese crown could not hide their low morale on account of the Pope's bull and the hopelessness of their resistance, as set down on letters to the King by the defenders.

[5]: 44  At this point, Ferdinand demanded a capitulation of Catherine and John III, but offered to negotiate their hold on the throne on condition that they sent their heir apparent Henry to be raised in the court of Castile.

The Navarrese leaders made a last stand at the Monjardin fortress under the control of Juan Vélaz de Medrano y Echauz, but eventually a capitulation was signed.

The loyalists retreated and the Castilian troops made their way back across the Pyrenees to Saint-Jean-Pied-de-Port and Lower Navarre, engaging in regular skirmishes with the disgruntled Beaumont party Lord of Luxe.

On 7 December 1512, a detachment of the Navarrese army's decimated landsknechts who were escorting twelve artillery pieces when they encountered a patrol led by the governor of Gipuzkoa Juan de Silva at the Belate pass.

Between 13 and 23 March 1513 the Parliament of Navarre, reduced to the Beaumount party representatives who had sided with the Castilian conquest, was called and accepted Ferdinand as their "natural lord and king."

Once the Castilian and Aragonese military confirmed their occupation of all the strongholds, the ground was paved for a progressive institutional takeover marked by the centralizing drive of the Spanish-Castilian Crown.

The diplomat and writer Niccolò Machiavelli anticipated a prompt and easy understanding by Ferdinand II with France "on the only condition of keeping Navarre, giving up instead the Duchy of Milan for its vicinity to the Helvetians.

Both scholars were acting as servants of their masters King Ferdinand II and the Duke of Alba when they accepted these propaganda assignments, as pointed out by the historian Alfredo Floristan.

[3]: 27  With Pamplona on his hands and the royal family in Béarn, Ferdinand further justified his claim on the Crown of Navarre by de iure propio, entitlement in his own right.

[7]: 19  The Papal ruling Pastor Ille Caelestis issued on 21 July, just three days after the start of the invasion, authorized Ferdinand to wage war on Church enemies and to claim their lands and subjects providing they lie outside Italy, which would apply to Louis XII's France and the "heretic" crown of Navarre.

Once Ferdinand II of Aragon died in January, the Parliament of Navarre gathered in Pamplona, urging Charles V, aged 16, to attend a coronation ceremony in the town following tradition.

The Duke was responsible for guarding the Navarrese lands conquered in 1512, but he had moved the bulk of his troops away from Navarre to suppress the Revolt of the Comuneros in his home territory of Castile.

[5]: 81–82  As the Franco-Navarrese army approached Pamplona, the citizens revolted and besieged the Castilian military governor, Ignatius of Loyola,[citation needed] in his newly built castle.

The troops of Guillaume Gouffier then headed to Labourd and on to Behobia, capturing the fortress of Urantzu and moving on to invest the coastal stronghold of Hondarribia (Fuenterrabía, Fontarabie) at the tip of Gipuzkoa in the Basque Country.

Ahead of the Castilian expedition to the Bidasoa, a combination of Gipuzkoan militias supported by 1,000 landsknecht engaged the Franco-Navarrese at the fortress of Urantzu in the Battle of San Marcial.

After the capitulation of Amaiur, orders were issued by the Venetian-born Castilian bishop of Pamplona, John de Rena, to level the fortress and pull down a number houses owned by Agramont sympathisers, as well as setting fire to the Abbey of Urdazubi.

At the peak of Francis' and Henry II's campaign, the Navarrese king made a symbolic gesture: he called the Estates of Navarre in Saint-Palais (Donapaleu), reuniting on 18 August 1523 at the church of Saint-Paul.

[5]: 104 The Viceroy of Aragon advanced to Oloron in Béarn and laid siege to the town, while the army of the Prince of Orange Philibert of Chalon failed to take Bayonne.

Balanza asserted that there existed "so much evil" in a number of southern Pyrenean valleys—starting from Salazar and Roncal, to Burguete (Auritz), Baztan, Bortziriak, Malerreka (to Pamplona)—located in the rear of the St-Jean-Pied-de-Port front in Lower Navarre, and an active theatre of war just a few years or months before, "it should not be only me who is aware of it".

To that end, he tried to marry his son and successor Philip II of Spain to the heir-apparent of Navarre, Jeanne d'Albret, in 1539, highlighting her high educational background and intelligence.