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The Blocksize War (2015-2017)

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The Blocksize War (2015–2017)

Tags: history, governance, SegWit, Bitcoin-Cash, UASF

Overview

The Blocksize War was a two-year conflict (2015–2017) over how to scale Bitcoin. Large blockers (miners, some businesses) wanted to increase the base block size limit (1MB) via a hard fork. Small blockers (developers, full node operators, most users) preferred a soft fork (SegWit) and Layer 2 scaling (Lightning). Small blockers won decisively.

Source: blocksize-war] (Jonathan Bier’s authoritative account)

The Core Dispute

Large blockers argued:

  • Bitcoin must scale on-chain to serve as peer-to-peer cash
  • 1MB blocks create fee pressure that will make small transactions uneconomic
  • Hard fork is technically straightforward; miners support it
  • Bitcoin Core developers are blocking necessary upgrades

Small blockers argued:

  • Increasing block size increases full node costs, reducing decentralization
  • A hard fork requires unanimous agreement — far too risky
  • SegWit (soft fork) increases effective capacity while fixing transaction malleability
  • Lightning Network handles small payments; base layer settles large/final transactions
  • Miners don’t have the right to change consensus rules unilaterally

Key Events

2015:

  • Scaling Bitcoin conferences (Montreal) organized to find solutions
  • Bitcoin XT proposed by Mike Hearn and Gavin Andresen: 8MB hard fork
  • XT gains modest support then fades

Feb 2016 — Hong Kong Roundtable:

  • Secret meeting of miners and developers
  • Miners agree to support SegWit if developers commit to 2MB hard fork after
  • Agreement collapses — developers did not consider it binding

Apr 2016 — Bitcoin Classic:

  • 2MB hard fork client; gains exchange/miner support briefly
  • Nodes crash when hit with large blocks from test
  • Movement collapses

Apr 2017 — ASICBoost:

  • Bitmain’s mining hardware had a covert optimization (ASICBoost) incompatible with SegWit
  • This explained why Bitmain was blocking SegWit despite agreeing to it in principle
  • Exposed by Gregory Maxwell

May 2017 — New York Agreement (NYA):

  • Barry Silbert organizes meeting of 58 companies (exchanges, miners)
  • Agreement: activate SegWit + commit to 2MB hard fork (SegWit2x) within 6 months
  • No major Bitcoin Core developers sign

Aug 1, 2017 — Two forks:

  • UASF (BIP148) activates: full node operators enforce SegWit rules; miners capitulate
  • Bitcoin Cash launches: Roger Ver and Jihan Wu create 8MB hard fork chain; market immediately assigns it ~10% of Bitcoin’s value (it fell further over time)

Aug 24, 2017: SegWit officially activates on Bitcoin mainnet.

Nov 2017: SegWit2x cancelled due to massive community opposition. Email to signatories reads: “Our goal has always been a smooth upgrade for Bitcoin. Although we strongly believe in the need for a larger blocksize, there is something we believe is even more important: keeping the community together.”

What the War Proved

  1. Full nodes are supreme: miners cannot change consensus rules without full node adoption
  2. Economic majority matters: exchanges and businesses that followed SegWit determined the “real Bitcoin”
  3. UASF works: users can force protocol changes by threatening to reject non-compliant miners
  4. Hard forks are nearly impossible: even with 58 major companies and major miners, SegWit2x failed
  5. Bitcoin Cash is an alt: the hard fork chain was immediately valued far below Bitcoin, confirming the market’s preference

Craig Wright

During the conflict, Craig Wright claimed to be Satoshi Nakamoto and threw his support behind large blockers. His claims were comprehensively disproven — he could not produce a valid signature from known Satoshi addresses. He later sued various Bitcoin community members for defamation (litigation ongoing). His involvement damaged the large-blocker cause by association.

Legacy

The blocksize war established the template for Bitcoin governance: changes require genuine consensus, soft forks are strongly preferred over hard forks, and full nodes (not miners) are the ultimate arbiters of Bitcoin’s rules. The SegWit activation also enabled the Lightning Network, which launched shortly after.

Sources

Glossary | governance | SegWit | Lightning Network | Satoshi Nakamoto | The Blocksize War (book) | timeline

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