In 1931, he founded the review journal Zentralblatt für Mathematik und ihre Grenzgebiete (Zbl), his most important contribution to modern mathematics. When Adolf Hitler became chancellor in 1933, Neugebauer was asked to sign an oath of loyalty to the new German government, but he refused and was promptly suspended from employment. In 1934, he joined the University of Copenhagen as a full professor of mathematics. In 1936, he published a paper on the method of dating and analyzing texts using diophantine equations. During 1935–1937, he published a corpus of texts named "Mathematische Keilschrift-Texte" (MKT). MKT was a colossal work, in size, detail, and depth, and its contents showed that Babylonian mathematics far surpassed anything one could imagine from a knowledge of Egyptian and Greek mathematics. He was an Invited Speaker of the ICM in 1928 in Bologna and a Plenary Speaker of the ICM in 1936 in Oslo.