began his military career in 1773 as a "distinguished" soldier in the Dragones de la Frontera cavalry regiment of the Spanish Army.
He took with him a small contingent, named the "disciplined troops" (Spanish: Tropas Disciplinadas), composed of 200 infantry soldiers and 100 Dragones de la Frontera cavalry.
They arrived to Buenos Aires on June 16, where they supported José de San Martín and the creation of the Second Triumvirate during the revolution of October 8.
In April 1813, Alcázar requested permission from the governing body of the United Provinces of the Río de la Plata to return to Chile together with his troop, in order to help in the defense of the country.
The troops left Buenos Aires on April 18, crossed the Andes at the end of May and arrived to Santiago on June 4, where was received with wild enthusiasm.