As Allied troops moved across Europe in a series of offensives against Nazi Germany, they began to encounter tens of thousands of concentration camp prisoners. Many of these prisoners had survived forced marches into the interior of Germany from camps in occupied Poland. These prisoners were suffering from starvation and disease.

Soviet forces were the first to approach a major Nazi camp, reaching Majdanek near Lublin, Poland, in July 1944. Surprised by the rapid Soviet advance, the Germans attempted to hide the evidence of mass murder by demolishing the camp. Camp staff set fire to the large crematorium used to burn bodies of murdered prisoners, but in the hasty evacuation the gas chambers were left standing. In the summer of 1944, the Soviets also overran the sites of the Belzec, Sobibor, and Treblinka killing centers. The Germans had dismantled these camps in 1943, after most of the Jews of Poland had already been killed.

In the following months after the liberation of Auscwitz in January 27, 1945, the Soviets liberated additional camps in the Baltic states and in Poland. Shortly before Germany's surrender, Soviet forces liberated the Stutthof, Sachsenhausen, and Ravensbrueck concentration camps.  

General Dwight D. Eisenhower and General Troy Middleton

Tour the Newly Liberated Ohrdruf Concentration Camp in Germany, April 12, 1945

US forces liberated the Buchenwald concentration camp near Weimar, Germany, on April 11, 1945, a few days after the Nazis began evacuating the camp. On the day of liberation, an underground prisoner resistance organization seized control of Buchenwald to prevent atrocities by the retreating camp guards. American forces liberated more than 20,000 prisoners at Buchenwald. They also liberated Dora-Mittelbau, Flossenbürg, Dachau, and Mauthausen.

British forces liberated concentration camps in northern Germany, including Neuengamme and Bergen-Belsen. They entered the Bergen-Belsen concentration camp, near Celle, in mid-April 1945. Some 60,000 prisoners, most in critical condition because of a typhus epidemic, were found alive. More than 10,000 of them died from the effects of malnutrition or disease within a few weeks of liberation.

Liberators confronted unspeakable conditions in the Nazi camps, where piles of corpses lay unburied. Only after the liberation of these camps was the full scope of Nazi horrors exposed to the world. The small percentage of inmates who survived resembled skeletons because of the demands of forced labor and the lack of food, compounded by months and years of maltreatment. Many were so weak that they could hardly move.

Disease remained an ever-present danger, and many of the camps had to be burned down to prevent the spread of epidemics. Survivors of the camps faced a long and difficult road to recovery.

Alfred Hitchcock directed a harrowing documentary about the Holocaust for the British military after World War II, but the project was suppressed by the British government. Hollywood director Brett Ratner has produced a powerful new documentary that uncovers an unknown chapter in film — and world — history.   HBO will air the film on January 26-27, to coincide with the 70th anniversary of the liberation of Auschwitz.

Click Here to See Trailer

After WWII ended in Europe, the British government trained a group of soldiers as cameramen to document the atrocities uncovered by ­Allied soldiers in Nazi concentration camps.  The graphic, firsthand footage was to be used as evidence against Germany, and Alfred Hitchcock was asked to direct the movie, called "German Concentration Camps Factual Survey." Hitchcock agreed and began in 1945. But just before his film was ultimately completed, the British government shut it down as Winston Churchill left office and the UK sought to ally with Germany against the Soviet Union.

Ratner's doc "Night Will Fall," about the lost film's history — which features some of Hitchcock's original footage as well as interviews with the men who shot it — screened at the Museum of Jewish Heritage on January 15, 2015.  

An emotional Ratner appeared near tears introducing the project. "The saddest thing is that the survivors of the Holocaust here today have to watch events 70 years later, like the atrocities in France," he said, referring to the recent Kosher-market attack in Paris. 

Directed by Andre Singer and narrated by Helena Bonham Carter, "Night Will Fall" describes how Allied forces trained soldiers to use the cameras, and how the results were hundreds of hours of firsthand footage of inconceivable suffering by Jews and other groups at Bergen-Belsen, Dachau, Auschwitz and more camps.