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Sarmiento's defining accomplishment during his tenure at El Progreso was his literary masterpiece, "Facundo." This seminal work, published in 1845, delved into the dichotomy of Argentina's socio-political landscape, pitting the civilized, progressive urban centers against the untamed, barbaric rural territories. Sarmiento's eloquent critique and his impassioned plea for societal transformation cemented Facundo's place as a cornerstone of Argentine literature and solidified his status as a prominent intellectual and social visionary.