Käthe Kollwitz was 47 when her 18-year-old son, Peter, was killed on Flanders Fields, in 1914. The grieving mother began using her platform as one of Germany’s most celebrated artists, noted for her masterful drawing and printmaking, to become one of its most outspoken pacifists. In 1918, when a newspaper article written by the poet Richard Dehmel called for more German troops to be sent to the Western Front, Kollwitz responded with an open letter begging for an end to the Great War and the loss of any more human life.

Kollwitz selecting pieces for her exhibition at the Prussian Academy of Arts, in Berlin, circa 1927.

“Seed corn must not be ground,” Kollwitz wrote in the same letter, taking inspiration from a line by Goethe. Come 1941, amid a second World War, the artist returned to this theme to make one of her last works of art, a crayon lithograph entitled Seed for Sowing Should Not Be Milled. The print, which depicts an old woman—Kollwitz died four years later at the age of 77—enveloping three boys in a protective mantle, is one of the highlights of “Käthe Kollwitz,” a timely retrospective opening at New York’s Museum of Modern Art on March 31.