During World War I, Jesenice ironworks were mainly converted to the manufacturers of military products for Germans. With the front lines being some distance to the south, the war did not reach Jesenice, which only suffered one bombing attack by Italian aircraft, with no casualties. With the end of World War I came major political changes; on December 1, 1918, the Kingdom of Yugoslavia was formed, opening up new markets. Due to its border position, Jesenice became an important traffic junction. Between the wars, first grammar school was established in 1914. The first "boys' and girls' school" was established in 1920, offering higher education. Jesenice was also the center of various kinds of craft and small trade. A tradesman's union was formed in 1920. Development of the ironworks continued; 4,567 workers were affiliated to a greater or lesser extent with KID by 1937.