It's not just the economic factors, though of course those are very important, it's the other stuff that comes with trade like stronger familial and social ties

It's not just the economic factors, though of course those are very important, it's the other stuff that comes with trade like stronger familial and social ties, joint cultural appreciation, and so on, that bind together countries more closely. Absent boarder disputes or mass immigration countries with trade and joint problem solving (e.g., climate change) tend to get closer over time.