Mises addresses the issue directly. In Omnipotent Government, he criticizes the eminent Spanish liberal Salvador de Madariaga for his opposition to Catalonian independence. “If some peoples pretend that history or geography gives them the right to subjugate other races, nations, or peoples, there can be no peace. It is unbelievable how deep-rooted these vicious ideas of hegemony, domination, and oppression are even among the most distinguished contemporaries. Señor Salvador de Madariaga condemns the demands of the Catalans and the Basques for independence, and advocates Castilian hegemony for racial, historical, geographical, linguistic, religious, and economic considerations.”
Attempts to suppress the autonomy of a distinct linguistic group, Mises thought, would tend to lead to war. Peace requires that groups be allowed to choose their own destiny. “It is futile to advance historical or geographical reasons in support of political ambitions which cannot stand the criticism of democratic principles. Democratic government can safeguard peace and international cooperation because it does not aim at the oppression of other peoples.”
Mises extended the right of secession very far: any group wishing to fend for itself should be free to do so. “The right of self-determination in regard to the question of membership in a state thus means: whenever the inhabitants of a particular territory, whether it be a single village, a whole district, or a series of adjacent districts, make it known, by a freely conducted plebiscite, that they no longer wish to remain united to the state to which they belong at the time, but wish either to form an independent state or to attach themselves to some other state, their wishes are to be respected and complied with. ... If it were in any way possible to grant this right of self-determination to every individual person, it would have to be done.”
Mises would have little sympathy for the view, held by some libertarians today, that Catalonian independence should be opposed because the Spanish government is at present less socialist than the Catalonian provincial authorities.