The Commonwealth Minutemen are one of the four fractions that appears in Fallout 4. They are a group of standard militia whose intention is to protect the people of the commonwealth "in a minute's notice".
The Minutemen were founded in the year 2180 A.D., 110 years after the thermonuclear bomb was dropped on the commonwealth and 100 years before the events of the Fallout 4. They were formed after a defenseless community was attacked by a group of super mutants, during which several volunteers stood up and defeated the mutants. As a result, these volunteers formed a local militia whose intention was to protect the people of the commonwealth from various threats "in a minute's notice".
Although it is unknown whom the original general the Minutemen was, there have been at least two generals prior to the events of Fallout 4: General McGann, who served until 2240, and General Becker, who served until 2282.
Prior to 2287, the Minutemen had a long, successful run; but after Becker's death in 2282, the groups luck and respect began to turn against them.
In 2287, Colonel Hollis and Preston Garvey received a call for help from a man named Sturges, who requested assistance against an attack by a mercenary group known as the Gunners, an event foreseen by the local "oracle" named Mama Murphy. Upon reaching the community, it was revealed that a fellow Minutemen named Clint betrayed the group and sided with the Gunners, which eventually overran the town, killing Hollis, and forcing Preston Garvey and nineteen other survivors of the massacre to flee.
Eventually the group began to dwindle in numbers. By the time the group had left the nearby Jamaica Plain, there were only ten survivors remaining. They eventually made their way to Lexington and finally Concord, there the survivors were pinned to the local Museum of Freedom, where they were ambushed by raiders. The day prior to the Sole Survivor's arrival, the Minutemen's numbers dropped eight, and at the time of the Survivor's arrival, only five remain: Preston Garvey, Sturges, Mama Murphy, and Marcy and Jun Long.
The Minutemen are generally the first of the four fractions encountered in the Commonwealth by the Sole Survivor. They are located inside the Museum of Freedom located in the town of Concord. There, the remaining five members are pinned in a small room located in the back of the building on the top floor.
The Sole Survivor must clear the museum of raiders while proceeding up to the room, there Preston Garvey, now the unofficial leader of the Minutemen will greet the survivor positively, stating that their timing was "impeccable". He will then order the survivor to collect a fusion core and install it into a set of power armor located on the roof of the building, then use it to dismantle a minion turret from a crashed vertibird and use it to clear the remaining raiders and a deathclaw located outside the museum on the streets of Concord.
Once all enemies are cleared, Preston will thank the survivor for their help and request their help in finding a new settlement. If accepted, the Minutemen will travel to Sanctuary Hills (the home of the Sole Survivor), and establish a new outpost there.
Over the course of time, Preston will assign the Sole Survivor several missions to establish new settlements within the Commonwealth as well as gain the support of settlements that already exist.
For settlements that already have settlers, the survivor must help the settlement leader with a mission before they decided to join the Minutemen, in most cases it is usually clearing out a nearby hostile outpost filled with raiders, gunners, super mutants, or ghouls, although sometimes it maybe a broader objective.
For unestablished settlements, the survivor is required to clear the area of any hostiles and build a radio beacon within the grounds. This requires construction of a generator as well in order to power the beacon. Once built, settlers will gradually begin arriving on the newly-establish settlement.
Taking Back the Castle
Eventually, after establish several settlements, Preston will assign the survivor with an important mission to help him retake Fort Independence (known as "The Castle") for the Minutemen, sit has been infested by mire mirelurks. He will meet the survivor outside the fort in a small diner where he, the survivor, and three other minutemen will discuss how they will attack the mirklurks, by a frontal attack or by a sneak attack.
Once the strategy is chosen, the Minutemen charge the fort and destroy all the mirelurks and their eggs, before confronting a Mirelurk Queen. The group successfully slays the giant monster, and afterwards Preston assigns the survivor the task of reactivating the Radio Freedom beacon; this task requires the construction of two medium generators. Once accomplished, Radio Freedom will spring to life once more and begin broadcasting emergency messages and American folk songs, and the Castle will officially be reclaimed by the Minutemen.
Opening the Barracks and Testing New Artillery
After more settlements have been established, Preston will task the survivor to return to the Castle once more. There, they will meet a stubborn, but charismatic woman named Ronnie Shaw, who has decided to rejoin the Minutemen after going separate ways for some time. She will task the survivor to reopen the sealed weapons barracks located on the west side of the fort via taking a secret tunnel located underneath the fort.
The survivor must clear the entrance to the tunnel and make their way through the tight passageways, which are filled with traps and a renegade sentry bot named Sarge. Once Sarge is defeated, Ronnie and the survivor enters the barracks and opens the entrance.
Ronnie will then tell the survivor to pick up some smoke grenades and some blueprints located inside the barracks and use them to build and test some artillery shells on the small diner outside the fort. The test is a success and Ronnie thanks the survivor for their help.
Infiltrating and Destroying the Institute
Once banished from the Institute, if the survivor decides to side with the Minutemen, Sturges will request the survivor to infiltrate the Institute by an unlikely entrance: a small sewage tunnel located southwest of Bunker Hill and enter the Institute stealthily.
Once inside, the survivor must access the terminal located at the location where they entered the Institute for the first time and use a holotype to override the controls and allow Preston, Sturges,and the Minutemen to enter the Institute. The group must then travel through a secret facility leading to the Bioscience wing of the Institute, destroying synths and minimizing casualties on the scientists.
Once the main atrium is secured, Sturges will tell the Survivor through the intercom that they must make their way towards the main reactor, however the passage leading to it is locked. Sturges instructs the survivor to locate the main terminal, which happens to be located in Father's room.
Upon entering the room, the survivor will encounter Father Shaun (the survivor's son) who is currently dying from cancer. The survivor will enter a conversation with Shaun, who will criticize the player, for going against the Institute, claiming that they had their chance to attempt to save his life and that Commonwealth is now truly doomed without them. The survivor will then state why they are destroying the Institute, and have the option to ask Shaun for one final request to save the surviving synths inside the Institute; this task requires a decent charisma level in order to succeed and is also required if the survivor wants to stay in good terms with the Railroad. Once accomplished, Shaun will give them the password to his terminal (which can also be hacked with a novice level), and use it to open the gate leading to the reactor, initiate evacuation orders, and shut down several of the synths inside the Institute. As the survivor leaves, they have one final option to either kill Shaun or leave him to die [not so] peacefully.
Once the gate leading to the reactor is opened, the survivor, Preston, and several Minutemen make their way into the reactor, where they have one final skirmish when several hostile synths and place a detonation device onto the reactor. Once completed, they are teleported back to the entrance of the Institute, where Sturges tells the survivor that a boy suddenly appeared just before the group was about to leave, claiming that they are the survivor's child, but is actually a synth version of Shaun. When confronted, the survivor may choose either to allow synth Shaun to travel back to the Commonwealth with them, or leave them to die.
Once the decision to spare or leave synth Shaun is made, Sturges teleports everyone out of the Institute into the roof of the Mass Fusion Building in downtown Boston. There, Preston will give the survivor the honor of activating the detonation device, which when triggered will destroy the Institute and the building located above it in a nuclear explosion.
After the Institute is destroyed, Preston, as well as any companions presented at the destruction, will comment above the events, most of which will react positively.