Block Size War

Bitcoin's block-size war ran from roughly 2015 to August 2017 and decided what kind of system Bitcoin would become. The flashpoint was a 1 MB cap Satoshi had added in 2010 as anti-spam scaffolding. By 2015 blocks were starting to fill, fees were rising, and two camps had calcified.

Big-blockers (Bitcoin XT, Bitcoin Classic, Bitcoin Unlimited, and later Bitcoin Cash) argued the cap should be raised — to 2 MB, 8 MB, or unlimited — to keep on-chain payments cheap. They were backed by most major mining pools and several large exchanges. Their flagship advocates were Gavin Andresen, Mike Hearn, Roger Ver, and Jihan Wu (Bitmain).

Small-blockers argued that the cap was load-bearing for *node decentralization*: bigger blocks raise the cost of running a full node, which centralizes who can verify the chain. They preferred scaling via off-chain layers ([Lightning](/glossary/lightning)) and witness-data restructuring ([SegWit](/glossary/segwit)). Their voices were Bitcoin Core developers, Pieter Wuille, Greg Maxwell, Adam Back, and a long tail of users running their own nodes.

The war ended with the User-Activated Soft Fork (UASF) of August 2017. Users — not miners — signaled that they would orphan any block that didn't enforce SegWit. Miners capitulated within weeks. SegWit activated. The big-blocker faction split off into Bitcoin Cash, which subsequently split again, again, and again. Bitcoin's block-size cap remained, in effect, where it was.

The deep lesson wasn't technical; it was political. The protocol's rules belong to whoever runs a node and enforces them. Hashrate is downstream of that, not upstream. Bitcoin came out the other side with a clarified social contract: hard forks for backwards-incompatible changes are nearly impossible, and the conservative default is the strong default.