[Update: New messages from the Fallout 4 teaser site confirm Massachusetts & the fall of Vault 119.]
In Fallout’s fiction the Commonwealth’s were formed when the nation was split into 13 sections somewhere around the last half of the 20th century. The New England Commonwealth was formed of Maine, New Hampshire, Vermont, Rhode Island, Connecticut and Massachusetts – of which Boston is the capital. After the war it emerged as prominent power known simply as the Commonwealth. It’s been mentioned in passing in both Fallout 3 and Fallout New Vegas, and by all accounts it is not a great place to be. Save, that is, for the mysterious and highly technologically advanced Institute.