He volunteered in the army with beginning of the World War, but soon distanced himself from the pro-war sentiment after being introduced to socialist ideas.
Together with Carl Max Maedge and Gertrud Savelsberg, he also belonged to the circle of friends and students around Ferdinand Tönnies, whom he knew from his time in Kiel.
[2] After the Nazi seizure of power and according to the Law for the Restoration of the Professional Civil Service, Meusel was forcibly dismissed from his position at the RWTH Aachen University for his political views and was taken in to protective custody for a short period.
In 1947 he became a member of the Presidential Council of the German Cultural Association and a full professor of modern history at what later became the Humboldt University in Berlin.
Being one of the few professors from the Weimar Republic who worked in the GDR, he was held in high esteem in East German universities and among SED politicians.