Talia/Miranda Tate wouldn't have destroyed Gotham City when she infiltrated Wayne Enterprises between The Dark Knight and The Dark Knight Rises, since Bruce Wayne supposedly rid Gotham of criminal control. As Miranda Tate she invested in Bruce's clean energy project but he enraged her by mothballing it 5 years in. Bane set up his lair beneath Applied Sciences and recruited people from the lower class of Gotham City to his army, they ran a Coup in West Africa, and crashed the plane in the beginning so Bane can retrieve Dr.Pavel.

Since Bruce refused to use the reactor(understandably), and Bane found Gordon's letter discovering the truth about the Dent Act; they decided to exploit it to torture Gotham City and Bruce Wayne.

Source-The Dark Knight Rises IMDB FAQ

Talia/Miranda Tate wouldn't have destroyed Gotham City when she infiltrated Wayne Enterprises between The Dark Knight and The Dark Knight Rises, since Bruce Wayne supposedly rid Gotham of criminal control. As Miranda Tate she invested in Bruce's clean energy project but he enraged her by mothballing it 5 years in. Bane set up his lair beneath Applied Sciences and recruited people from the lower class of Gotham City to his army, they ran a Coup in West Africa, and crashed the plane in the beginning so Bane can retrieve Dr.Pavel.

Since Bruce refused to use the reactor  (understandably), and Bane found Gordon's letter discovering the truth about the Dent Act; they decided to exploit it to torture Gotham City and Bruce Wayne.

Source-The Dark Knight Rises IMDB FAQ