[2] His golden hour came, and he rose dramatically to the occasion, when at aged 37 and as Bolivian Army chief he united the pro-Velasco and pro-Santa Cruz factions under his command to face-off a massive Peruvian invasion led by President Agustín Gamarra.

However, to stave any revolutionary plots by the rebellious Colonel Belzu and José Miguel de Velasco, Ballivián appointed military officers that supported him, like Dámaso Bilbao la Vieja and Eusebio Guilarte, in positions of power.

Generally, he followed the organizational and administrative style of Santa Cruz and took great care to keep his supporters happy, thus positioning himself as the Grand Marshal's heir.

However, he failed to create a credible deterrent military presence in the area, since he tended to concentrate loyal troops in the important centers of population in order to quell rebellions, especially after 1845.

[4] Ballivián had the misfortune of experiencing the defection, and subsequent dogged personal opposition, of the charismatic General Manuel Belzu, once head of the Army but now wounded by the alleged or perceived pursuit of his wife by the President.