Why Bitcoin May Split In Two

UASF will force activation of SegWit in the bitcoin blockchain, that will increase the block size and fix more issues which will make transactions faster in simple words. Without majority hash rate it will cause a serious chain split
That's how there's a possibility of 2 versions

About USAF :

https://www.reddit.com/r/Bitcoin/comments/64jky9/what_is_uasf/

This has happened in the past with Ethereum in a different situation.
This is not impossible. However, it is highly unlikely.

More info

http://www.forbes.com/sites/laurashin/2017/04/04/why-bitcoin-may-split-in-two-and-how-to-prevent-it/

http://www.slate.com/articles/technology/future_tense/2017/06/internal_conflict_could_split_bitcoin_in_half.html

https://www.reddit.com/r/Bitcoin/comments/64jky9/what_is_uasf/

https://cointelegraph.com/explained/segwit-explained