Or basically as a TL:DR
The Second amendment was supposed to ensure that
US Population > US army
in a fire fight.
This changed after the US got it's ass kicked a couple times by indians and the British, leading to a larger and larger standing government army.
Then after the US got it's ass kicked by it's own citizens when it tried to infringe on their rights... it slowly took away the right to bear arms from it's citizens.