Probably the troops guarding them.
The first death camp to become operational was Chelmno on 8 December 1941. (In this context I assume that death camprefers to a camp intended entirely or almost entirely for killing).
This death camp was the first liberated by the Allies.
Saratoga
After Anne Frank's death, the concentration camp where she was held, Bergen-Belsen, was liberated by British troops in April 1945. The camp was later torn down and a memorial was built to honor the victims.
The first camp to be freed was Majdanek, which was actually in the city of Lublin in Poland. Part of it was an 'ordinary' concentration camp, the other part was an extermination camp (death camp). It was freed by Soviet forces on 22 July 1944.
The First 48 - 2004 Return to Sender Death Camp 8-2 was released on: USA: 8 January 2009
An outlying camp of the Buchenwald system, Ohrdruf, was the first Nazi camp liberated, on April 4, 1945, by the US 89th Infantry. The remainder were liberated by April 12, but not before SS troops tried to remove or kill off some inmates of the main camp beginning on April 8. In response, the camp's prisoners mounted a successful takeover of the camp on April 9. The first US Army personnel (6th Armored Division) entered the main camp on April 11, 1945.
There was no battle at Valley Forge. It was the winter camp for Washington's troops and park service historians have proven that the men did not starve, die, nor freeze to death. Washington "spun" his letters to Congress to keep the funding of the troops up. He was afraid that if Congress knew how well they were doing they would cut back on funds for his troops.
Ohio Colored Troops at Camp Alger - 1903 was released on: USA: January 1903
yes
"The military deploys its troops by spreading them out across the battle field to confront the enemy head on and to avoid being surrounded as the war is being waged", Master Sargent Henry told his new recruits on their first day in boot camp.
Yes, all the camps in Poland and other Eastern European were liberated by the Soviet Army.