In the War of the Pyrenees against the French, Juan Mackenna fought in Rosselló under General Ricardos and there met the future liberator of Argentina, José de San Martín.

Once in Lima, he contacted Ambrosio O'Higgins, another Irishman, at that time Viceroy of Perú, who named him Governor of Osorno and put him in charge of the reconstruction works for this southern Chilean town.

His successful administration provoked jealousy from Chile's captain-general Gabriel de Avilés, who feared that Juan Mackenna and Ambrosio O'Higgins would create an Irish colony in Osorno.

Both Irishmen were loyal to the Spanish crown, though Juan Mackenna had good relations with O'Higgins' son Bernardo, the future emancipator of Chile, and was also connected with the Venezuelan Francisco de Miranda and his group of supporters of South American independence.

[2] A bust of General MacKenna was publicly presented to Monaghan County Museum on 5 August 2004 by his direct descendant es:Luis Valentín Ferrada.

Dr Joseph Duffy, Bishop of Clogher and by his descendant Senor Ferrada who declared, "In this city of Monaghan, very near to Willville House, the tombs of my ancestors are in the old cemetery.