there is always an increasing adoption of bitcoin which is constantly contributing to the long term rise of bitcoin price. last year this adoption was "booming" which is why the price also "boomed".
here are major incidents that contributed to this big rise:
- mainstream adoption of bitcoin in Japan. finally Japanese decided to officially accept bitcoin as a "legal method of payment" and that was a big move helping the rise a lot. mainly because of hundreds of merchants in Japan that started accepting bitcoin. this was also led to change of views in other countries even in Russia after years of negativity against bitcoin.
- removal of taxes on bitcoin payments. again in Japan and a couple of other countries like Australia. and you can imagine how merchants that were already accepting bitcoin and the new ones felt. which helps with the adoption.
- the end of 3 year scaling debate in August. finally the scaling debate which was a very big slow down for bitcoin's growth came to an end when the big blockers forked off and bitcoin could finally come to consensus and have Seregated Witness activated which also opened up lots of future possibilities such as Lightning Network, Cross Chain Transactions (Atomic Swap), more anonymity (Confidential Transactions), ...
- price rise itself. when bitcoin performs well and it is rising and giving a lot of profit, a lot of new investors become aware of it and start investing in it in order not to "miss the boat"
- a lot of publicity in the media which is practically advertising bitcoin!
Thanks for your insights - I wasn't aware of the huge adoption level in Japan (like removal of taxes). This and the media coverage on bit coin prise rise would have given lot of confidence for new investors to trust and invest in bit coin, which would have let to its meteoric rise!