Sameerishere answers Why don’t countries, like companies, more often merge?

[Sameerishere]

I haven’t studied this extensively, but I’d add to drachenfels’ answer that not only do leaders lack the desire to merge countries, but so do their citizens. Fundamentally, it seems that people are averse to giving up sovereignty/​autonomy over the policies that govern them, and merging reduces that sovereignty.

It would be interesting to consider how the United States and EU came to be in spite of this.