In 1915, Lieutenant John McCrae, a WW I medical officer from Guelph, Ontario, wrote the Poem “In Flanders Fields” on a scrap of paper following the death of a fellow soldier.
After the poem was published in a magazine, an American teacher named Moina Michael read it and was so inspired by it that she pledged to always wear a poppy as a sign of remembrance.
In 1920, a French woman named Madame Guerin learned of the custom. She decided to make and sell poppies to raise money for children in war-torn areas of France. The poppy was officially adopted the Flower of Remembrance on July 5, 1921. Read more about the poppy here.