user54433: I was looking to study the history of Bitcoin forks including the 2013 incident that may or may not have been a Hard fork depending on your definition.

user52820: There is a paper that provides extensive detail on the history of all kind of forks on Bitocin, Ethereum and Ethereum Classic, you can read it here, Atomically Trading with Roger: Gambling on the success of a hardfork.
Here is the list of Forks so far,

The following content is sourced from the above paper,

    So far, Bitcoin has implemented over six softforks. These softforks
range from introducing rules to prevent miners creating coinbase
transactions with duplicated identification hashes, requiring all
ECDSA signatures to strictly enforce DER coding, and introducing both
absolute and relative lock times for individual transaction outputs.
In terms of implementation, this involves storing new information in
the scriptsig of the coinbase transaction, constraining transaction
validation rules or re-defining the use of special OP_NOP function.
   On
the other hand, Bitcoin has experienced two accidental (and temporary)
splits (i.e. Fork-1, Fork-2 emerged) that required miner intervention
to remedy. The first split permitted a user to exploit an integer
overflow bug and create 184 billion coins. This required miners to
co-operatively extend a new blockchain without the coin creation
transaction [6] and to enforce a soft-fork to prevent this exploit.
The second split involved miners who upgraded to Bitcoin Core 0.8
accidentally creating blocks that were invalid for Bitcoin Core 0.7.
Unfortunately, BerkeleyDB’s configuration in Bitcoin Core 0.7 was
non-deterministic and as a result was not compatible with LevelDB’s
configuration in Bitcoin Core 0.8. Resolving this fork required miners
to immediately downgrade to Bitcoin Core 0.7 and abandon the forked
blockchain. Next, the developers released Bitcoin Core 8.1 that
enforced the activation of a hardfork12 after a two-month grace period
for miners and users to upgrade.


user47827: The best resource I've seen that answers this question is this BitMEX blog post. It includes some of the early Satoshi era forks that haven't been included in any existing answers.


54433: <p>I was looking to study the history of Bitcoin forks including the 2013 incident that may or may not have been a Hard fork depending on your definition.</p>
 52820: <p>There is a paper that provides extensive detail on the history of all kind of forks on Bitocin, Ethereum and Ethereum Classic, you can read it here, <em><strong><a href="https://web.archive.org/web/20171116062404/http://homepages.cs.ncl.ac.uk/patrick.mc-corry/atomically-trading-roger.pdf" rel="nofollow noreferrer">Atomically Trading with Roger: Gambling on the success of a hardfork</a></strong></em>.</p>
<p>Here is the list of Forks so far,</p>
<p><a href="https://i.stack.imgur.com/WEvvB.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/WEvvB.png" alt="enter image description here" /></a></p>
<p>The following content is sourced from the above paper,</p>
<blockquote>
<p>    So far, Bitcoin has implemented over six softforks. These softforks
range from introducing rules to prevent miners creating coinbase
transactions with duplicated identification hashes, requiring all
ECDSA signatures to strictly enforce DER coding, and introducing both
absolute and relative lock times for individual transaction outputs.
In terms of implementation, this involves storing new information in
the scriptsig of the coinbase transaction, constraining transaction
validation rules or re-defining the use of special OP_NOP function.<br />
   On
the other hand, Bitcoin has experienced two accidental (and temporary)
splits (i.e. Fork-1, Fork-2 emerged) that required miner intervention
to remedy. The first split permitted a user to exploit an integer
overflow bug and create 184 billion coins. This required miners to
co-operatively extend a new blockchain without the coin creation
transaction [6] and to enforce a soft-fork to prevent this exploit.
The second split involved miners who upgraded to Bitcoin Core 0.8
accidentally creating blocks that were invalid for Bitcoin Core 0.7.
Unfortunately, BerkeleyDB’s configuration in Bitcoin Core 0.7 was
non-deterministic and as a result was not compatible with LevelDB’s
configuration in Bitcoin Core 0.8. Resolving this fork required miners
to immediately downgrade to Bitcoin Core 0.7 and abandon the forked
blockchain. Next, the developers released Bitcoin Core 8.1 that
enforced the activation of a hardfork12 after a two-month grace period
for miners and users to upgrade.</p>
</blockquote>
 47827: <p>The best resource I've seen that answers this question is this BitMEX <a href="https://blog.bitmex.com/bitcoins-consensus-forks/" rel="nofollow noreferrer">blog post</a>. It includes some of the early Satoshi era forks that haven't been included in any existing answers.</p>
<p><a href="https://i.stack.imgur.com/GnAqI.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/GnAqI.png" alt="BitMEX table" /></a></p>
