They had their first success with an anthology of young American authors, American Harvest, following it up with an anthology of European writing, Heart of Europe, both in English. Despite almost insuperable financial difficulties, in addition to the rationing of paper after the U.S. entered the war, the two published - along with politically motivated analyses of the European situation in English and first books by American authors - a strong series of German-language volumes. Several volumes by Thomas Mann appeared with L.B. Fischer, including Joseph, der Ernährer, the last volume of the Joseph tetralogy, as well as books by Franz Werfel, Richard Beer-Hoffman, and many other authors in the paperback series Bücherreihe 'Neue Welt'.

During this period Landshoff, like Bermann Fischer, continued to direct European operations as best he could from the U.S., putting out many Dutch, English, and German books in Amsterdam throughout the war years. In 1946, after the sale of L.B. Fischer, Landshoff returned to Holland to continue publishing. In 1952 Harry N. Abrams invited him to join his firm as European representative. After 33 years, Landshoff retired as vice-president of the New York firm.