Reason..

 

Ukraine is terminating the Russian-Ukrainian Friendship Treaty of 1997. 
The treaty prevents Ukraine and Russia from invading one another's country respectively, and declaring war. 
On 19 September 2018, Ukrainian President Petro Poroshenko signed a decree not to extend the treaty. 

Ukraine announced its intention not to renew the treaty in September 2018. By doing so the treaty did expire on 31 March 2019. The treaty was also known as the "Big Treaty".

On 3 December 2018, Poroshenko drafted a legislation to Parliament to end the Treaty of Friendship immediately; with support coming from Western allies within the United Nations Security Council.

So who started the problem? May be both.

Who is loosing in this conflict? All countries who encouraged and supported the conflict.

 Just a thought.