Germany to another world

1971 and the vietnam war wages on. Germany and America join forces to fight and stop the spread of communism. Hans Hoffmen jr was drafted into the war. He and his troops fought until they were called back home emendently. For some reason they were not told why they called back so fast. When they came back a new building popped up. Then they were told to guard the unknown building. Then during one of their guarding hundreds of troops came flooding. They were soldiers wearing a roman like armor and weapons. Then the soldiers under Hoffmen command open fire and wipe out. After the incident the building/gate was badly damaged which caused it to close again before that happened a spy and his family were sent in to study the other side. Now in 2018 Colonel Wolf Hoffmen was in Berlin for an important meeting walking past the building which is now called the great gate. Then it happens all over again... Later he was told to take his forces and go through the gate.