World War I caused a crisis in the ethics of masculinity for North American Mennonites. It marked their first continent-wide forced contact with militant states involved in a popular mass war. As an internally divided, secluded, pacifist, and primarily German-speaking people, they were not prepared for the challenge the militant masculinity posed to Mennonite men. Mennonite teachings on the war were only consistent with masculine humility, not pacifism. The response of Mennonite men was complex and some men responded to the war by developing new concerns for church doctrine and for global relief work, trends that strengthened the Mennonite churches. However, the damaging impacts of the crisis are reflected in the demographic records of the Mennonite men who were still forming their masculinity at the time of the war. These records reveal earlier deaths, a higher ratio of marriages ended by the wife''s death, and higher levels of exogamy. The most startling effect was the changed sex ratio among their children, with a higher ratio of sons to daughters especially for the first born child. The earlier discursive failure in ethics correlated with a long term behavioural failure.