The Minutemen are a major faction in Fallout 4 and the first to be introduced in the main quest. However, the player's interactions and quests with the faction are not exactly that explorative when it comes to the Minutemen's actual history and complicated political past. There is far more to them than just helping people and forming relationships with settlements.
By the time players meet the faction in Fallout 4, much of the leadership and members have died. Preston Garvey is all that is left of the leadership before the protagonist is able to sign on to the group. This is in the year 2287, a hundred years after the Minutemen truly rose to prominence in the Commonwealth.
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The Minutemen first became a big deal in 2180, when they protected Diamond City against a large assault of super mutants. After gaining positive attention and trust with the people of the Commonwealth in the coming 50 years, they made an alliance with regional settlements and attempted to create a provisional government in the 2230s.
The Institute was going to be involved in this government, as they had not totally shut themselves off from the surface yet. However, they decided to back out. This led to the CPG Massacre Incident, with a synth killing all settlement representatives. This ended all future attempts to organize a united Commonwealth and began igniting the fear of the Institute.
It is unknown how long the Minutemen used Fort Independence as their base in Boston. They renamed it The Castle, and used it as their base and armory until 2240, when a mirelurk queen destroyed parts of the landmark. This killed their general at the time, General McGann, as he became trapped during the attack and died alone
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