Some very interesting comments by someone identified only as Z:
Graeber posits that actors buy T-bonds because the US has a central role in the world system and also notes that this central role is being contested; both by other industrial powers in the conventional economic sense and by a world movement in the political arena (I am not necessarily endorsing those claims, just trying to present Graeber’s thesis accurately). Confronted to these challenge to its central position, and seeing that its central position is crucial to the functioning of its economy (because it is in massive debt), the US has to maintain its predominance in one way or another. Now think about it as an economist: what is the one comparative advantage that the US has on the rest of the world? Obviously military power. So, on the short term, it might be tempting to US elites to try to organize the world around military power as a way to maintain their quite surprising position within the world economy. This, as I understand it, is Graeber’s thesis: not we buy T-bond because we fear we will be bombed but as long as the world is organized around geo-strategical lines, the US will be able to live off the rest of the world.