How do contentious hard forks actually happen?

[Heptapod]

A hard fork always causes a chain to split into two.  Who actually creates the new chain and how?  Is this just the development community?  How can a minority of the devs create a new coin if consensus is required to change the protocol?

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[achow101]

Who actually creates the new chain and how?

Anyone can create a chain split and hard fork. You do so by releasing software which has incompatible consensus rules with the current consensus rules.

Is this just the development community?  How can a minority of the devs create a new coin

It is not "the development community" but rather a specific group of developers. As I said, anyone can do whatever they want; it's an open source project, they can fork the source code and change it.

if consensus is required to change the protocol?

Consensus is not required to make a fork and an altcoin. Consensus is required to make a fork and have everyone agree that that fork is still called Bitcoin.

[Heptapod]

Ok that makes sense now, thanks so much for the detailed response.  So, aren't there many other Bitcoin forks that random people create just by copying the code and changing something?  Does this happen all the time and we just don't hear about it? 

[achow101]

Ok that makes sense now, thanks so much for the detailed response.  So, aren't there many other Bitcoin forks that random people create just by copying the code and changing something?  Does this happen all the time and we just don't hear about it? 

Yes. IIRC there have been several forks of Bitcoin but no one hears about them nor cares about them.

[janah]

Anyone can create a chain split and hard fork. You do so by releasing software which has incompatible consensus rules with the current consensus rules. An adding answer for this is to do sone research about the software and make sure it is valid and locked software so that you are safe.