D'Estournelles represented France at The Hague Peace Conference in 1899. He attempted to get acceptance for the principle of compulsory arbitration, but this was not possible. After the conference he strongly promoted the Permanent Court of Arbitration, and he founded the French Groupe de l'Arbitrage in 1903. D'Estournelles advocated Franco-German conciliation and wanted a European federation. In 1905 he founded Conciliation Internationale, a network of peace workers aimed at influencing public opinion. At the second conference at The Hague in 1907, d'Estournelles continued his work to strengthen international arbitration.