This article tackles the political confrontation that took place in Biscay between 1917 and 1923, which had important consequences in the historical evolution ofthe Basque Country. It is addressed through the electoral procedures that took place in those years. For the first time, Basque nationalism reached meaningful power and representativity shares, and won the 1917 and 1918 elections. A new period started - one characterized by tensions between Basque nationalism and Spanish nationalism (espanolismo), with alliances between royalists and leftists (republicans and socialists). In 1919, Basque nationalists lost their temporary political primacy. Ideological fights caused intense electoral clashes where the different groups used procedures that spoiled votes.