comment: >
  
  Russia signed the Budapest Memorandum in 1994, in which Russia guaranteed to respect the territorial integrity of Ukraine.
  Until Russia complies with that document which it signed in 1994, its signature on a new 'peace treaty' document is worthless.
context: Ukraine won't negotiate until it gets back all of its territories, and the Russians don't see Ukraine as a legitimate state. Diplomacy between the two is impossible.