[1] Back to Argentina, he joined the State of Buenos Aires army and took part in the battles of Cepeda and Pavon against the Argentine Confederation, where he reached the rank of captain and later of mayor.

[2][3] After a dispute between his superiors, General Wenceslao Paunero and Bartolome Mitre, regarding promotions, Mayer resigned to the army and in late 1861 he returned to the United States, where his uncle owned a store.

After he saved the life of French-appointed General Leonardo Márquez in the aftermath of the siege of Querétaro, in 1867, Mayer was set for execution by firing squad for treason.

[2] Mayer went back to Argentina in 1873, after a long trip across the United States (where he met Cuban patriot Jose Marti), Mexico, and Britain.

His rank of general was recognized by Carlos Tejedor, governor of Buenos Aires province, and in 1875 he commanded the rebel artillery during an uprising against the federal government, led by President Nicolas Avellaneda.

[10] Undeterred by a number of ill-fated investments in shore facilities and railways, Mayer eventually purchased a ranch in Santa Cruz, then a federal territory in Patagonia region.