I'm writing an assignment in school and would like some explanations on STASI along with relevant sources as my teacher expects me to cite where i found my information from.

Explain 3 key differences between STASI and SÄPO (Swedish intelligence agency, this is what the assignment says but the comparison can be made to any modern intelligence agency) I believe the teacher is talking about persecution and murder conducted by STASI

How was it possible for STASI to deploy so many agents to various countries around Europe? How can an organisation get such a large influence in a country? Why did so many cooperate with them?