Diplomacy has not worked, it didn't work after polonium, novichok or Crimea. It's big stick time time unfortunately.
Diplomacy didn't work after Iraq, Afghanistan, Libya, Syria, Somalia, or .. Yemen .. either. It didn't work to stop the murder of two million innocent people in Iraq, and it hasn't worked to stop genocide enacted by a totalitarian-authoritarian dictatorship, aligned with Al'Qaeda, and supported by the Wests' military-industrial complex. It didn't prevent the utter destruction of Mosul or Raqqa, and it hasn't stopped the funding and arming of known terrorist groups by Western NATO members, either.
Given that heinous track record, nobody wants to 'negotiate' with the West any longer, and that is quite understandable.
If you want to do something effective, get your OWN war criminals prosecuted for their crimes.
Inviting former parts of the Soviet Union to join NATO is not "diplomacy."[1]
The US should try this diplomacy with China: recognize Taiwan as an independent country, invite it to join NATO and see what the Chinese do.
[1] Blinken: Ukraine has all tools to move towards NATO membership (https://www.kyivpost.com/ukraine-politics/blinken-ukraine-ha...)
It is not like the world suddenly recognised it as a new country last week.
...which is looking less theoretical by the day.
NATO already made it pretty clear with Libya that sovereignty wasnt top among its list of concerns.