In 1931, he founded the review journal Zentralblatt für Mathematik und ihre Grenzgebiete (Zbl), his most important contribution to modern mathematics.[citation needed] 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.