Gabino Crispín Gaínza Fernández de Medrano (20 October 1753 – 1829) was a Spanish military officer, knight of the Order of St. John and prominent politician in Spain's American colonies.

[3] Gabino's grandfather Enrique was the son of Don Diego Fernández de Medrano y Zapata, Knight of the Order of Calatrava, Lord and divisero of Regajal, and governor of the province of Carrión in the valley of Atlixco in 1693 to 1706.

[12] Overseas, Gaínza embarked in the fleet of Lieutenant General Victorio de Navia, being detached from Havana to the Mobila garrison, now Mobile.

According to his own words, "not having been able to enter this place due to mishaps at sea, in which I ran a great risk, I headed for the province of Louisiana by way of the Mississippi River".

[13] Gaínza was later assigned to Havana, participated in various campaigns garrisoning the ships of the Barlovento Squadron, with actions in the Bahamas archipelago on the nao Paula, and made two trips to Guárico.

After Spain signed the treaty of Paris with Great Britain, Gabino Gaínza Fernández de Medrano went with his regiment to the Kingdom of Peru.

Corral and Gabino Gainza Fernández de Medrano departed from La Coruña, via Panama, Guayaquil, and Lima, and arrived in the Viceroyalty's capital in 1788, when Tupac Amaru had already been executed.

He crossed the Isthmus of Panama, where, due to the rugged terrain and the insane nature of the country, according to his own words, he suffered a serious breakdown in his health.

That year, he was promoted to Commander General of Trujillo in Peru, with the obligation to fortify and defend the northern coasts from English attacks, once again at war with Spain.

In 1799, he reinforced the military garrisons of the Santa Marta and Túmbez rivers, captured an English whaling frigate, destroyed a corsair schooner, and visited Guayaquil three times.

In 1804, Gaínza pacified the rebellious Indigenous peoples of Lambayeque, then became the Military Chief of the Province of Trujillo, fortified the port of Paita, and captured several English schooners.

He also entrusted Gaínza Fernandez de Medrano with convincing the insurgent army of Chile to lay down its arms and thus avoid bloodshed, under the promise of absolute pardon, and his oath of the monarch and of the new Constitution of Spain.

[17] As the new Royal Governor (Captain General) of Chile, Gabino Gainza Fernández de Medrano left the port of El Callao at the head of a force of 125 chosen men.

This was augmented by the addition of 700 militiamen from Chiloé, after the arrival in Chile, with fifteen hundred spears, money, tobacco, sugar, 5 artillerymen, and 2 cannons from his regiment, in the corvette Sebastiana and the brig Potrillo.

[18] The landing of Gaínza Fernández de Medrano in Arauco on 31 January 1814 could not be prevented by the troops of Bernardo O'Higgins, commander of the insurgents in this sector.

After arriving at Arauco Bay on the following 31 January and finding a Chiloé battalion there, he entered into relations with the main Mapuche leaders, celebrating with them at Parliament of Quilín, to whom Gaínza Fernandez de Medrano gave batons, medals and other gifts.

The following day (4 March), Gaínza Fernandez de Medrano received another stroke of luck from one of his militia units, commanded by Clemente Lataño.

Gabino Gaínza Fernandez de Medrano was victorious at Cancha Rayada on the 29th of the same month; he also expanded the royalist territory with the squares of Concepción and Talcahuano.

The treaty was signed on the banks of the Lircay River, about 7 kilometres (4.3 mi) outside the city of Talca by the commander of the Royal Armies in the province of Concepción, brigadier Gabino Gaínza Fernandez de Medrano, and the representatives of the Chilean Supreme Director Francisco de la Lastra, brigadiers Bernardo O'Higgins and Juan Mackenna.

On 9 March 1821 Lieutenant General Carlos Luis de Urrutia, in order to restore his health, which according to his own words had been quite ailing since the previous August, temporarily delegated command of the province in all its aspects to Brigadier Gabino Gaínza Fernandez de Medrano, deputy general director of the troops, in accordance with the Royal Order on the matter, which he communicated to the First Secretary of State on 18 March.

"[20] Article 2 states that the acceptance of the Leader (Gaínza Fernandez de Medrano) will have as its first effect the convocation of a General Assembly of residents (under the pretext of preventing disorder in case the people decide on independence), in which only those attending will be secretly proposed to vote for or against it.

[20] The Plan Pacífico document is significant because it clearly states in Article 7 that nothing will be changed regarding the government, and there will be no discussion of removing any employee unless they are considered a danger to the immediate future system.

It was then stated that if Gaínza Fernandez de Medrano accepts this position, he will proceed to the Cathedral to give thanks to the Most High, and the rest of the people will disperse throughout the city to make the corresponding demonstrations.

[20] Gabino Gaínza Fernandez de Medrano hastily called a meeting on the morning of 15 September 1821 at the National Palace of Guatemala.

At the meeting called by Gabino Gaínza Fernandez de Medrano, the declaration of independence was signed, which was approved with 23 votes in favor and 7 against.

There participated representatives of the government, municipality, Catholic Church, University of San Carlos, Trade Council, legal board among other groups.

On 29 October 1821 the president of the provisional governing council of newly independent Mexico, Agustín de Iturbide, sent a letter to Gaínza Fernández de Medrano (now the president of Central America) and the council of delegates representing the provinces of Chiapas, El Salvador, Honduras, Nicaragua and Costa Rica with a proposal that Central America join the Mexican Empire under the terms of the Three Guarantees of the Treaty of Córdoba.

Gaínza Fernandez de Medrano answered a month later, on 3 December 1821, that it was necessary to consult with various city governments in order to respond to the invitation.

The secretary of the consultative junta that advised Gaínza Fernandez de Medrano, Mariano Gálvez, was accused of having manipulated the results to favor annexation.

But it was also true that many towns (Comayagua, Ciudad Real, Quetzaltenango, Sololá, the intendencias of Nicaragua) joined the Empire on their own initiative, jumping over the chain of command that included Guatemala City.There was much pressure to adopt this decision.