The Blocksize War: The Battle Over Who Controls Bitcoin's Protocol Rules is a book by Jonathan Bier, published in 2021 (ISBN 978-9878463155). It provides the most detailed and comprehensive account of the Bitcoin scaling debate that consumed the Bitcoin community from approximately 2015 to 2017, culminating in the Bitcoin Cash hard fork and the activation of Segregated Witness.
Overview
The blocksize war was a conflict over a deceptively simple technical question: should Bitcoin's maximum block size be increased beyond the 1MB limit that had been in place since Bitcoin's early days? Behind that technical question lay much deeper disagreements about governance, Bitcoin's identity as a payment system versus a settlement layer, and who had the legitimate authority to change the protocol.
Bier, who followed the debate closely as it unfolded as a writer for BitMEX Research, traces the full arc of the conflict: from the early proposals to raise the block size limit, through the formation of competing camps, to the failed SegWit2x hard fork agreement and the creation of Bitcoin Cash in August 2017.
Key Themes
The book documents the arguments of both sides with care. The "big blockers" -- led by figures including Gavin Andresen, Roger Ver, and Jihan Wu -- argued that Bitcoin needed larger blocks to accommodate growing transaction demand, and that without increased capacity, high fees would price ordinary users off the network. They saw the small-block position as serving the interests of companies like Blockstream that had commercial interests in layer-two fee businesses.
The "small blockers" -- represented by most Bitcoin Core developers and much of the developer community -- argued that increasing the block size would centralize the network by making it more expensive to run full nodes, ultimately concentrating power over the blockchain in the hands of large mining operations. They advocated for Segregated Witness as a more elegant technical upgrade and for the Lightning Network as Bitcoin's scaling path.
The UASF Movement
One of the book's most compelling sections covers the User Activated Soft Fork (UASF) movement, in which ordinary Bitcoin users signaled through their node software that they would enforce SegWit activation regardless of miner signaling. The UASF demonstrated that economic nodes -- not just miners -- held significant power over protocol changes, a lesson that has shaped Bitcoin governance discussions ever since.
Historical Significance
The blocksize war is arguably the most consequential governance event in Bitcoin's history. Its resolution -- the rejection of large-block proposals, the activation of SegWit, the creation of Bitcoin Cash as a separate chain -- established that Bitcoin's protocol could resist pressure from well-funded corporate and mining interests when the broader user community was sufficiently mobilized.
Bier's account has become the definitive historical record of these events, providing essential context for anyone seeking to understand how Bitcoin's governance works and why Bitcoin's current design is what it is. The conflict also directly motivated Nicolas Dorier to create BTCPay Server as an open-source alternative to BitPay.
External Links
- The Blocksize War on Amazon
- The Blocksize War on Goodreads
- Bitcoin Scalability Problem on Wikipedia
- SegWit on Wikipedia
- BitMEX Research Blog
References
- Gavin Andresen -- key figure in the big-block camp
- Adam Back -- Blockstream CEO in the small-block camp
- Blockstream -- company central to the scaling debate
- Bitcoin Core -- the software whose governance was at stake
- Lightning Network -- the scaling solution advocated by small blockers
- Nicolas Dorier -- created BTCPay Server in response to the debate
- BTCPay Server -- born from the blocksize war