This is the 13020th most frequent Korean word.
동독에
"동독에" means "in East Germany."
Here, '동독에' indicates the location where the younger sibling was previously situated (East Germany).
동독에 있던 동생이 한국으로 돌아왔다.
My younger sibling who was in East Germany returned to Korea.
The context '동독에' in this sentence points to 'regarding East Germany', discussing the place as a topic.
동독에 관한 책을 읽어보았다.
I read a book about East Germany.
The phrase '동독에 대한' reflects the subject of the research being focused on East Germany.