On the outbreak of the Franco-German War he worked energetically to impede the projected alliance with France, and to drive the Lanza cabinet to Rome.
Sella, the real head of the Lanza cabinet, was worn out by four years continuous work and disheartened by the perfidious misrepresentation in which Italian politicians, particularly those of the Left, have ever excelled.
Had declared war on Prussia, and immediately afterwards he withdrew his troops from Civitavecchia; but he persuaded Lanza to promise to abide by the September convention, and it was not until after Worth and Gravelotte that he offered to give Italy a free hand to occupy Rome.
In 1867 he attempted unsuccessfully to form a cabinet sufficiently strong to prevent the threatened Garibaldian incursion into the papal states, and two years later failed in a similar attempt, through disagreement with Lanza concerning the army estimates.
Although unarmed, the people rallied to him as one man, and Lanza became so alarmed that he asked for an unconditional extension of the armistice, which Garibaldi granted.
The dictator now had time to collect ammunition, and the Neapolitan government having given Lanza full powers to treat with him, 15,000 Bourbon troops embarked for Naples on the 7th of June, leaving the revolutionists masters of the situation.
Commerce at Genoa had urged the Lanza cabinet to establish a commercial depot on the Red Sea.
Though an ardent supporter of the historic Right, and, as such, entrusted by the Lanza cabinet with the defence of the law of guarantees in 1870, he was no respecter of persons, his caustic tongue sparing neither friend nor foe.