Whereas companies often undergo a friendly merger or acquisition, why don't countries more often do this? Set aside colonialism because I'd like to focus on the case where the threat of violence is not paramount.
I suppose the right incentives aren't in place but is this an intrinsic fact of international relations or democratic politics?
For example, a merger between the US and Mexico seems, naively, like it could be in both nations' interest. The US gets more land and lower-cost labor and Mexico gets access to better governance and knowledge spillover.