Two developers, nullc and pieter are against increasing the blocksize at a reasonable rate. Gavin, Jeff Garzik and Mike Hearn wish to increase it by early next year. Following some three months of debate, an agreement could not be reached, so Gavin and Mike are forking Bitcoin to the new Bitcoin XT. The vast majority of users, businesses and miners support Gavin and his bigger blocks, but blockstream, a relativley new for profit company which employs nullc aka Gregory Maxwell and Pieter as well as some other bitcoin devs and is developind lightning and sidechains which they offer as an alternative to increasing the blocksize has managed to stall this process, thus leading to a fork.