Head smashing was also present enough in episode 5x09 to give us reason to believe Negan is around. When Noah found his old house, he found his mother with her head smashed in the living room. Very similar to what Negan did to Glenn.
A trade-off is a situation where you make a compromise between two things, or where you exchange all or part of one thing for another. ...the trade-off between inflation and unemployment. American English: trade-off
International trade theories are simply different theories to explain international trade. Trade is the concept of exchanging goods and services between two people or entities. International trade is then the concept of this exchange between people or entities in two different countries.