～なければならない and ～によって auxiliary meanings

Question

I am having trouble with the bold part of this sentence from wikipedia:

バブル経済（バブルけいざい、economic bubble）とは、概ね不動産や株式をはじめとした時価資産の資産価格が投機によって実体経済の経済成長以上のペースで高騰し続け、投機によって支えなければならない市場が、投機によって支えきれなくなるまでの経済状態を指す。

The best I can get for the bolded text is:

The state of the market that needs to be propped up by speculation until it can no longer be supported by speculation.

This use of ～なければならない　combined with ～によって is hard for me to translate. Since によって is repeated twice, I am curious if this is some special grammatical construct. In particular it seems that ～なければならない here might mean not 'needs to be propped up', but something else, since logically the markets do not require themselves to be propped up. I'm probably just missing something basic. Please give me a translation and explanation.

Answer 1

The way I interpret that sentence is:

バブル経済（バブルけいざい、economic bubble）とは、概ね不動産や株式をはじめとした時価資産の資産価格が投機によって実体経済の経済成長以上のペースで高騰し続け、投機によって支えなければならない市場が、投機によって支えきれなくなるまでの経済状態を指す。

An economic bubble denotes economic conditions where, due to speculation, a steep increase in the present value of assets including to a great extent real estate and stocks continues at a pace exceeding the growth of the actual economy, and the market which must be sustained by speculation ends up becoming unsustainable by speculation.

Basically what I think it's trying to say is the speculation leads to a vicious cycle that can't be sustained.

Edit: Tried to fix the translation.