 After the outbreak of World War I, Sienkiewicz was visited at Oblęgorek by a Polish Legions cavalry unit under Bolesław Wieniawa-Długoszowski. Soon after, he left for Switzerland. Together with Ignacy Paderewski and Erazm Piltz, he established an organization for Polish war relief. He also supported the work of the Red Cross. Otherwise, he eschewed politics, through shortly before his death he endorsed the Act of 5th November 1916, a declaration by Emperors Wilhelm II of Germany and Franz Joseph of Austria, pledging the creation of a Kingdom of Poland envisioned as a puppet state allied with, and controlled by, the Central Powers.
