Both Hitler and Stalin were both military geniuses although their evils tend to heavily outweigh their good deeds. They were both expert propogandists and were amoral and willing to do whatever they could to better their country, they were also both quite paranoid and good strategists.
Their expert propoganda skills came into play to allow them to both attain and keep power. Hitler has been described as the world's greatest propogandist saying that he was nearly able to brainwash people with his words. Their propoganda skills were also the reason they were able to commit the atrocious acts they commited without being overthrown. It seems they were very smart to be able to control their people like this.
Another quality they both had in common was their complete and utter lack of morals. Hitler had no grief when he sent millions of Jews to concentration camps, nor did Stain feel any anguish as he killed thousands upon thousands of his fellow countrymen, both of these acts had another thing in common. They were both done for the good of the Mother/Fatherland. This shows that both men had extreme pride in their countries and would do literally anything to make them a stronger country although not necessarily a nicer place to live in.
Another similarity they had between them was their exteme paranoia, with Stalin eradicating most of his commanding officers shortly before WW2. Hitler was plagued with various mental illnesses and temporay spouts of blindness caused by a mustard gas injury he recieved in WW1. This caused Hitler to be quite suspicious of anyone.
While they were both very odd men, no one can say that were not extremely smart in the military operations, both of them running strong, effiecient militaries, which they used to conquer much of Europe, they were both quite found of infantry based warfare, Hitler invented the Blitzkrieg, or "lightning war" which he used to quickly capture a good chunk of Eureope....