The following year, Schwimmer was hired as a press secretary of the International Woman Suffrage Alliance in London. When World War I broke out, she was branded an enemy alien and left Europe for the United States, where she spoke on suffrage and pacifism. She was one of the founders of the Woman's Peace Party and the organization which would become the Women's International League for Peace and Freedom. In 1915, after attending the International Congress of Women in The Hague, she worked with other feminists to persuade foreign ministers in Europe to support the creation of a body to peacefully mediate world affairs and was instrumental in convincing Henry Ford to charter the Peace Ship. From 1916 to 1918, Schwimmer lived in Europe working on various plans to end the war. With the establishment of the First Hungarian Republic, she was appointed as one of the world's first female ambassadors (from Hungary to Switzerland) in 1918. When the Republic was toppled by a "coup d'état", she fled to the United States, renouncing her Hungarian citizenship.