He was twice imprisoned during World War I for so-called patriotic activities. He left Laeken in 1919 and dedicated himself to social work from then on. In August 1914 he gathered food and medicine for soldiers and war victims. He was arrested in November 1916 and sentenced to thirteen months imprisonment on 6 December; his mother suffered a nervous breakdown upon learning of this. Cardijin used his time in prison to read the Bible and Karl Marx and smuggled his writings out of prison. In turn he received books and other materials through the underground. He was arrested again in 1918 on an espionage charge and sentenced to a decade of hard labor but was released following the November 1918 armistice that ended the war. In 1919 he suffered from tuberculosis due to his imprisonment and was sent to Cannes in France for several months of recuperation before going back to Belgium. In 1919 he started the ("Young Trade Unionists"). This group at first met resistance from within the Church but after a while the organization and Cardijn became accepted; in fact Cardijn received a blessing from Pope Pius XI in March 1925 who encouraged his work. Following their meeting the pope said: "Here at last is someone who comes to speak to me about the masses!" adding that "the Church needs the workers and the workers need the Church". In an autographed letter in 1935 the pope backed the Jocistas as an "authentic model" for activism and social action. He received permission in 1924 from Cardinal Mercier to meet the pope with Clemente Micara (the then nuncio to Belgium) helping to facilitate the March 1925 meeting. The pope blessed the movement and affirmed that "we make it our own!" He and the pope met again in 1927. The noted theologian Yves Congar likened the pope's approval for Cardijin's movement as reminiscent of that of Pope Innocent III confirming the Order of Friars Minor for Saint Francis of Assisi centuries prior.