Excerpt From Summary of Jonathan Bier's The Blocksize War
#1
On August 15, 2015, two of the most prominent and respected Bitcoin developers, Mike Hearn and Gavin Andresen, released their own versions of the software, called Bitcoin XT and Bitcoin Core, respectively. Many within the community were upset about the division within the community.
#2
On the surface, the conflict seemed to be centered around the size of blocks in the Bitcoin blockchain, but in reality, it went much deeper.