Russia has signed https://en.wikipedia.org/wiki/Russian%E2%80%93Ukrainian_Friendship_Treaty https://en.wikipedia.org/wiki/Russian%E2%80%93Ukrainian_Frie... in 1

Russia has signed https://en.wikipedia.org/wiki/Russian%E2%80%93Ukrainian_Friendship_Treaty https://en.wikipedia.org/wiki/Russian%E2%80%93Ukrainian_Frie... in 1999 As mentioned in article 2, the High Contracting Parties shall respect each other′s territorial integrity and reaffirm the inviolability of the borders existing between them