In his textbook Contemporary World History what does Duiker mean when he says that the trend toward globalization may be offset by a simultaneous trend toward fragmentation?
What Duiker means when he says this is that the move towards globalization may not be the only move going on in the world. There may be a move going in the opposite direction. This is the move towards fragmentation. Duiker says that the move towards fragmentation might be stronger than the move towards globalization.
The move towards globalization is well-known. Many scholars believe that this move will make the people of the world grow more and more similar to one another. There will, they say, come to be a relatively global culture where things like ethnicity and nationality will not matter much.
But others argue that there is a different movement happening. This is the kind of movement that (one can argue) we see towards isolation and nationalism in the US today. Today, we worry about globalization and the way that it takes our jobs and sends them to China. Or we worry about the way that it brings illegal immigrants into our country. In response, we "fragment" ourselves and start thinking about the world in terms of "us" versus "them." We start to trust the rest of the world less because it seems threatening.
This is what Duiker is saying, that this second movement may end up being stronger than the first movement.