Montgomery agonized over the battles of the First World War. She was living in Leaskdale, Ontario, as a Presbyterian minister's wife, and she was meant to provide comfort and support for parishioners. Twenty-one young men from the extended parish served in the war; six of them were killed (SJ,II,xv). She dedicated Rainbow Valley (1919) to three young Leaskdale soldiers "who made the supreme sacrifice that the happy valleys of their home land might be kept sacred from the ravage of the invader." The war was immediate and personal and affected daily life profoundly.

Every day Montgomery read the War Summary and the detailed news in The Globe. In her journal, she wrote hundreds of pages documenting the major campaigns of the war and talked about the impact of the war on the home front. On 5 August 1914 she began "England has declared war on Germany! Good God, I cannot believe it! It must be a horrible dream. It has come up like a thundercloud" (SJ,II,150). She did not believe the war would end quickly and, like many of her contemporaries, saw it as a death struggle between good and evil. When news came over the telephone in 1918 that Germany had sued for peace on President Wilson's terms, Montgomery wrote in capital letters in her journal "SUNDAY, OCTOBER 6, 1918 It should be written in capitals--in letters of gold" (SJ,II,269).

In her journals she recorded the horror or suspense she felt over Flanders, Verdun, Vimy, Passchendaele, the Marne, over the sinking of the Lusitania and the Halifax Explosion. When she wrote Rilla of Ingleside (1920), a novel describing the heroism involved in daily life during the four years of the war, she drew directly from her journals. This novel is the only fictional war-time account by a woman describing the home front in Canada. Putting the novel together with the journals--and now with the --gives a very vivid picture of Canada in war time.