[C] happens because of the fact that the Financial District turns the possibilities of all the people on its area of influence into Midas Money, which makes its destruction a large-scale reality-bending phenomenon. Reality is altered so that the records and memories pertaining to the land, countries and people that disappeared due to the reality-bending have never existed in the first place. An example of that is the disappearance of Carribean Republic, which existed between Central America and the Carribean Islands before the [C] of its Financial District.
After the conclusion of the first stage, comprising the reality-bending phenomenon, [C] begins its second stage, in which surrounding countries and economical markets are thrown into instability, diminishing the creditworthiness of those regions and causing a chain reaction that initiates more reality-bending phenomenon to occur. It may even cause the [C] of other regions.