(Devarim 19:8) "And if the L-rd your G-d broaden your border": Do the mitzvah stated herein, in reward for which the L-rd will broaden your border.
"as He swore to your forefathers" — all in the merit of the forefathers.
"and He give you all the land that He swore to give to your forefathers": These are (the cities of) the Keni, the Kenizi, and the Kadmoni (across the Jordan, where three cities of refuge were established).