Short answers, pulled from the story.
East Germany, officially the German Democratic Republic, was founded on the 7th of October 1949 and ceased to exist on the 3rd of October 1990, when its five states joined the Federal Republic of Germany after forty-one years as a separate state.
The Stasi was East Germany's Ministry of State Security, responsible for surveillance and repression of the population. At the end of the GDR in 1990, approximately one hundred and nine thousand informants were still active. The International Rehabilitation Council for Torture Victims estimates between three hundred thousand and five hundred thousand victims of Stasi abuses.
East Germany built the Berlin Wall beginning on the night of the 12th of August 1961 to stop mass emigration to the West. About one quarter of East Germans had already left before the Wall was completed, and because many emigrants were young and educated, the economy was severely weakened by the population loss.
A sequence of events in 1989 led to the fall. Hungary removed its border fence with Austria on the 2nd of May 1989, allowing East Germans to flee west. The Pan-European Picnic near Sopron on the 19th of August 1989 produced the largest mass escape from East Germany since 1961. Massive protests, including an estimated three hundred thousand people in Leipzig and half a million in East Berlin on the 4th of November, forced the government's hand, and sections of the Wall were opened on the 9th of November 1989.
Despite paying substantial war reparations to the Soviet Union, the GDR built the most successful economy in the Eastern Bloc. In 1976, average annual GDP growth was five percent, and the estimated 1984 per capita income was nine thousand eight hundred dollars. By 1985, state and collective enterprises earned ninety-seven percent of the net national income.
Zersetzung, meaning decomposition, was the Stasi's primary method of repression under Erich Honecker from 1971 onward. It involved sending offensive mail, spreading malicious rumors, sabotaging careers, banning travel, and breaking into homes and moving objects to cause psychological disorientation. Between 1985 and 1988, the Stasi conducted roughly four thousand five hundred to five thousand such operational cases per year.