The Soviet Union, for a flagrant disregard for human rights both before, after and during the war
Although the Soviet Union suffered the highest number of casualties in the Second World War some of the worst atrocities in history were carried out by the Soviet Union around the time of the Second World War. Furthermore, the Soviet Union's rejection of Imperial Russia’s signing of The Hague Convention served to justify them in committing numerous war crimes. This also served to rationalise the mistreatment of Red Army POWs by the Nazis, in much the same ways as the formidable reputation of the imperial Japanese army encouraged Allied soldiers to become increasingly brutal over time.
Prior to the onset of the Second World War the Soviet Union, under the paranoid authoritative dictatorship of Joesph Stalin, a long string of some of the worst crimes against humanity had already been committed. After taking power forcefully in 1924 following the death of Vladimir Lenin, Stalin quickly began a large scale campaign of political repression, that lead to 1,500,000 arrests and over 600,000 deaths. Most historians agree that throughout the 1930’s alone Stalin’s actions, and indeed criminal negligence, lead to the deaths to somewhere between 9 and 11 million people. This estimate combines direct repressive killings by the Stalin regime, premature deaths of the extensive prison, concentration camp, and exiled citizen population, and unthinkable amount of planned starvation, the worst of which being the Holodomor in Ukraine.
The Soviet Union were involved in the beginning of the war, signing a mutual non-aggression pact with the nazi’s and then extending their territories to include, Lithuania, Latvia, Estonia, parts of Romania and East Poland. This came with a large number of massacres in this new territory as Stalin had begun implementing a scorched Earth policy in 1941.
The total number of life lost at the hands of the Soviet Union is highly debated and very difficult to attribute an accurate number to. The wide scale and level of violence, torture, starvation and disappearances are so far reaching it is almost unfathomable, this makes the Soviet Union the worst country not only in World War Two but quite possibly in the history or war.