The age-sex structure of a population is directly affected by war casualties, which mainly affect males in the younger age groups. Wars also affect age structure because of the indirect effect they have on fertility.
During a war, men in the armed forces are separated from their wives for long periods; and this inhibits fertility. In the immediate post-war period, however, there is often a “baby boom” because couples unite once again, and marriages, postponed because of the war, are solemnised.
The age-sex pyramid as affected as the smaller-sized cohorts during the war and the bigger-sized cohorts after the war move upwards with the passage of time.