Start by clearing up through "Act II - A Whisper or a Roar" in the storyline. None of the side-missions are necessary up to that point (aka the black mini-map icons).
After this mission, you'll need to enter Paris Area 2 and meet an old woman named Margot Bonaire ([Ma] icon). You'll complete the "Act II - Jailbreak" mission for her. Afterward, you'll gain access to Margot's side-storyline. It consists of three missions: "Fahreinheit Four Fifty...", "Bulletproof", and "Symphony of Destruction". After the final one, you'll inspire a large chunk of Paris Area 2.
Then, just continue the storyline for one more mission ("Act II - The Big Gun") and you'll inspire the remainder of Paris Area 2 and receive the achievement!