World War I and the disappearance of the Austro-Hungarian Monarchy from the political stage of Central Europe disrupted a great segment of the then social relations. In the same way that the Agrarian Reform expropriated landowners from their estates (i.e. they no longer had the right to freely use their land), houseowners in Croatia were likewise dispossessed by the enactment of various rules and regulations. Upon his arrival in Zagreb from Bosnia in 1920, Pilar found countless desperate houseowners without any means whatsoever. Namely, up to 1914 it was believed — and rightly so — that building housing blocks was the best possible investment sure to bring in secure rent. Yet, in the newly constituted Yugoslavia this was no longer so. Pilar assumed the office of secretary of the Houseowners’ and Landowners’ Association in Zagreb, as well as that of secretary of the Houseowners’ and Landowners’ Savings and Loans Cooperative. Until his death he fought for the restoration of ownership rights, all the while referring to the legal standards of Europe that the new state had previously committed itself to meet. Owing to Pilar’s exceptional competence and professional knowledge, his struggle ended with great success on the eve of the so-called January 6th Dictatorship. Full ownership was returned to houseowners. The Agrarian Reform Liquidation Act from 1931 also restored partial ownership to landowners. Pilar’s expertly written papers succeeded in changing the negative attitudes on ownership rights developed under the influence of the Russian Revolution, and the communists and social democrats in Croatia. He groundedly proved that “affluence and ownership are not theft” and thus restored faith in the profitability of capital investments by private entrepreneurs in the construction of residential buildings. Owing to his efforts, another cycle of intensive investment in building began. Because of his dedication to legally protect private ownership of residential buildings Pilar came into grave conflict with the Croatian communists. Relying on European legal regulations he secured full ownership to houseowners in Croatia and forced the authorities to respect the universally accepted standards.