In his meeting with Zelenskyy in the Oval Office, Trump briefly said
I could tell you right now there's a nation thinking about going to war on something that nobody in this room has ever even heard about. Two smaller nations—but big, still big—and I think I've stopped it, but this should have never happened. (source)
What nation is he referring to? Why would they want to go to war? My guess is he's referring to Armenia, but I'm not sure.
Without verifiable details it's impossible to be sure if his claim is factually correct, or even grounded in consensus reality. He may have been pointing at a genuine potential conflict where he feels like he de-escalated something, or he may have been storytelling to flex his power (real or imagined) as a peacemaker. The countries could be real or imagined, the de-escalation could be real or imagined.
From the context, my guess is that regardless of the reality of these "two smaller nations", he was merely employing a plot device to tell Zelenskyy, "War is always bad (and you might be implicitly bad for allowing Ukraine to be involved in one). You should just give Russia what it wants so Russia stops hurting Ukraine with war." He doesn't need real nations for that persuasion tactic, and speculating on the identity of these possibly-fictional nations might be a distraction.
Interesting that he would suggest Russia's invasion of Ukraine should be resolved the same way as when a mugger demands your wallet. But that seems (to me) to be what he's suggesting here.
I'm saying that since we know that "facts" offered by Trump to support his goals aren't always true, that part of his conversation with Zelenskyy is probably best viewed as part of a persuasion tactic that may or may not be factually connected with reality.