German President Frank-Walter Steinmeier spoke at the German-Russian museum in Berlin-Karlshorst on Friday to commemorate the 80th anniversary of Nazi Germany's invasion of the Soviet Union during World War II.

The museum is located in the same building where the German Wehrmacht signed the unconditional surrender to representatives of the Soviet Union, the United States, Great Britain and France on May 8, 1945.

"Nobody during this war mourned more victims than the people of the former Soviet Union," Steinmeier said, adding that the German war against the Soviets was carried out with "murderous barbarity."

"It weighs on us that our fathers, grandfathers, great-grandfathers who waged this war, were involved in these crimes," he added. 

Steinmeier's remarks opened an exhibition at the museum called, "Dimensions of a Crime:  Soviet Prisoners of War in World War II." The Wehrmacht captured around 5.7 million Soviet prisoners of war, of whom 3 million died in captivity.

On Monday, Steinmeier visited the Sandbostel camp in the northern state of Lower Saxony, a former prisoner-of-war camp that today is a memorial site. Steinmeier spoke with former prisoners and laid a wreath.

On Tuesday, June 22, a wreath-laying ceremony is scheduled at the Soviet War Memorial in Berlin-Pankow.

Representatives from 15 ex-Soviet states were invited to Friday's exhibition. Ukrainian Ambassador Andrij Melnyk rejected the invitation, calling the museum venue "an affront" because of its "Russian" focus and because the wartime persecution of other countries such as Ukraine, Belarus and the Baltic states was being "simply ignored."

What was Operation Barbarossa?

On June 22, 1941, Nazi Germany launched its invasion of the former Soviet Union, which was code-named Operation Barbarossa.

The attack involved 3.3 million troops along an 1,800-mile (2,900-kilometer) front, making it one of the largest invasion forces in history.

Adolf Hitler famously broke the non-aggression pact, known as the Molotov-Ribbentrop pact, signed in secret between Nazi Germany and the Soviet Union weeks before the war began in August 1939.

The German invasion less than two years later caught the Soviets by surprise, and their forces were initially overwhelmed and incurred heavy losses before consolidating to block the German offensive.

Eastern Europe's WWII killing fields 

Operation Barbarossa opened the Eastern Front in Europe, the largest of the entire war, which witnessed some of its fiercest battles and worst atrocities until Nazi Germany's capitulation in May 1945.

An estimated 30 million people were killed on the Eastern Front — far more than any other theater during World War II.

Soviet civilians in areas under Nazi occupation in Eastern Europe were subjected to brutal and arbitrary killings. Nazi racial ideology targeted both Jews and Slavs, millions of whom were executed or sent to concentration camps.  

"From the first day the German campaign was driven by hatred, by antisemitism and anti-Bolshevism, by racist madness against the Slavic and Asian peoples of the Soviet Union," Steinmeier said. 

"Those who waged this war killed in every possible way, with unprecedented brutality and cruelty," he added. "It was German barbarism, it cost millions of lives and devastated the continent."

Learning from history

Steinmeier's office said in a statement that the series of memorial events this week is intended to draw attention to the suffering of the Soviet Union, which at 27 million incurred the highest number of casualties during World War II, 14 million of whom were civilians.

"And yet these millions are not as deeply burned into our collective memory as their suffering and our responsibility require," Steinmeier said.

He added that after the war, many Germans did not want to hear about the wartime suffering of people in the Soviet Union, whose story had been obscured by the Cold War and the division of Europe behind the Iron Curtain.

"Only those who learn to read the traces of the past in the present will be able to contribute to a future that avoids wars, rejects tyranny and enables peaceful coexistence in freedom," Steinmeier said Friday.