What is the Reason for increase of the Bitcoin?
This is due to the very high demand of bitcoin in the market with respect to the supply available. I believed that this event was greatly influenced by the announcement of Japan that they will accept bitcoin as a mode of payment and this was last April 2017. Followed by Russia, then the most current is the announcement of Australia. Announcing such acceptance surely brings huge number of new users, thus, increasing the demand for bitcoin tremendously.
I agree there is no doubt that these countries you stated are aggressively buying bitcoin. Well, we can not blame them since several major companies stated that bitcoin is the current "hot money" meaning, there is a huge potential of profit gain when they involve in bitcoin. Aside from that South Korea also pushes bitcoin price to $2350. This means South Korea are taking part for bitcoin price increase.