If you watch the credits of the first one, at the end is sort of a prequel to the 2nd one. for Tokyo Drift, it has Dom in the end of it. then in the 4th one, because of what Brian did in 2, his record is clean, so he can get a job with the FBI. At the end of that one, he breaks Dom out of a transport so he is on the run again, which brings us to the 5th one.