电影《柏林墙以东》的历史背景是什么？

简介：Felix, a West-Berlin resident, falls in love with Thomas, an East-German citizen, who lives in Berlin. They maintain their relationship through regular visits to each other, but the strict curfew regulations force Felix to return every evening. When the authorities in East Germany become suspicious about Felix's frequent visits and his connection to Thomas, they begin to investigate. The authorities suspect that Felix is harboring illegal immigrants and plan to deport them both to the West. To protect himself and his lover, Thomas decides to try and flee to the West. He contacts Felix and tells him of his plans. However, Felix refuses to let Thomas go without him, as he believes Thomas deserves to stay in Berlin and face the consequences of his actio…