Imagine being famous because of how perfectly you can judge enemy intentions only to choke at a moment like this

Was he even good at diplomacy? Can’t shake this feeling he was never good at that.

In 1813, Napoleon’s situation was to put it mildly horrendous. Nearly all Europe was united against him. The nations of Russia, Austria, Spain, Sweden, Prussia, Britain and other small powers were all militarily fighting, his armies had been decimated and were outnumbered 4:1 across Europe, his allies were all invaded/occupied, as were his vassals, and

However, recognizing that an invasion was not a sure thing (The allies had not managed to defeat france in the first and second coalitions either, despite having key advantages such as much higher internal unrest ) Therefore, the Frankfurt proposal was sent. This would reduce France to its ‘natural frontiers’, which was more or less just modern day France and Belgium.

However, Napoleon severely misjudged the intentions of this proposal. This was frankly the best possible deal Napoleon could hope for, in fact many nations and their key commanders, notably Prussia were outraged at the generous deal. However, he thought this was the start of negotiations, that this was a standard lowball offer, and so attempted to parlay to keep certain key fortified German cities, to secure the Rhine border.

This was seen throughout Europe and even in parts of France as Napoleon having lost his sense of reality. Beliving that Napoleon ws never going to be reasonable and would fight to the end, the allies cancelled the deal, and invaded France, ending the war the year after in his defeat.

It would have never led to a long lasting peace, Napoleon was seen as a threat to the traditional monarchies and I’m pretty sure the UK weren’t part of the proposal either which would have been problematic at some point.
Even if he said yes there would have been a war in next few years, that’s certain