The books included biographies of Friedrich Schiller, Frederick the Great, and Prince Eugen, as well as novels such as Ein Volk wacht auf ("A People Awakes", 1918–21).
Although von Molo, a pacifist, had no Jewish forebears, he defended the Jews of Germany and Austria, and with the rise of Nazism he repeatedly drew the anger of anti-Semitic organizations.
In October he was one of the 88 German writers who went so far as to subscribe to the Vow of Most Faithful Allegiance (Gelöbnis treuester Gefolgschaft) to Adolf Hitler.
During the World War II he wrote articles for the Nazi-controlled newspaper Krakauer Zeitung published in occupied Kraków.
Although Molo's biography of Frederick II of Prussia was praised by the Nazis, he nevertheless came under attack as unvölkisch, ein Judenfreund and Pazifist (he had, for example, effusively praised the work of Erich Maria Remarque), and there were attempts to push him from public life, with the banning of plays, and the suppression of certain books and their removal from libraries.
As a result of the harassment, he destroyed, with the help of his second wife Anne Marie, a large part of his private library, including correspondence with Stefan Zweig, books by Thomas and Heinrich Mann bearing personal dedications, and many papers of his colleagues.
On 4 August 1945 an open letter from Molo to Thomas Mann, begging him to return from the United States, was published in the Hessischen Post and other newspapers both in Germany and abroad: "Your people, hungering and suffering for a third of a century, has in its innermost core nothing in common with all the misdeeds and crimes, the shameful horrors and lies...." His sentiments were echoed by Frank Thiess, whose own piece would popularise the use of the phrase innere Emigration to describe the choice of some intellectuals to remain in Germany, a phrase Mann himself had used in 1933.