I just Googled Charles Roburn, and all of the links it comes up with are about... you guessed it... Diplomacy.
I suspect it's not a metaphor for anything, although certainly one can read various things/images/allusions/etc into anything if one wishes.
As an example off the top of my head:
This poem is a shocking indictment on the human condition, dealing as it does with religious paranoia, Western organised religion vs Eastern mysticism, the interminable nature of the moment immediately prior to a final decision, and the terrible human weaknesses engendered therein.
'Monsieur and Pontiff, I will bet,/Are safe. They can't invade me... yet' could be an allusion to the Great Schism in the Roman Catholic, a period during which (IIRC) there were two Popes, one in Rome and one in France (at one point, I believe there was a third - possibly in Constantinople?). Clearly, the author regards Christianity as being somewhat non-threatening, however this is only due to the 'lack of common borders' between the author and Christianity. This is a comment on established religion's tendency to despise things that are similar to their own manner of thought. For example, history shows us countless examples of Christianity waging war on Judaism and Islam (or vice versa in any combination) despite that they believe in the same God. Christianity, however, does not wage war on Buddhism or Shinto, which have radically different characteristics.
Indeed, the author expresses fear only of his neighbours, and also self-loathing over the necessity to befriend one.
By distancing himself from Christianity in this way, and his dismissal of martial solutions ('defenseless Russian realm'), Roburn aligns himself with the philosophical systems of the East. Roburn's reticence to choose an ally finds resonance in the varied Buddhist ideologies, which share the common thread of the path to Enlightenment being inward. This is directly at odds with Roburn's assertion that he needs to ally with one of his neighbours lest his 'dream of empire end'.
The melancholy tone of the final stanza indicates that, like Hamlet, or Prufrock, the author does not relish the thought of committing to a course of action. The central issue of the poem is the resolution of this particular choice, and yet we only realise this at the end, giving the previous twelve lines an air of rambling, hesitating procrastination.
His hesitation in this regard belies a lack of faith in his own convictions. He desperately wishes to have the strength of will to believe that the path to greater glory is inwards, however he does not have the courage to pursue this course of action.
Oh dear. I clearly need to go back to sleep.
Please be assured that my tongue was firmly ensconced in my cheek.
