Why did Greenspan say this about Treasury yields?

Because if China suddenly unloads it's 1.1 Trillion in U.S. Treasuries in the Trade War going on, it would also create below zero Treasury yields around the world too. And Since Treasuries are the main way the U.S. carries it's Federal Debts it could be a fiscal disaster for the U.S. and lead to an actual bloody war with the U.S. if the U.S. is hurt bad enough and goes into another Great Depression at that point as a nation. This would be an INTERNATIONAL disaster of epic proportions and smaller nations would be destroyed in the fallout too economically in a chain reaction if China did this. At this point a violent war of some kind could easily break out in retaliation towards China for doing this.