<< It was toxic financial derivatives (not) backed by fraudulent liar’s loan mortgages (“green slime”) that drove the U.S. crisis.>>
A reaction, make that reactive malfeasance, not the cause.
The cause was the government interfering with traditional (and sound) mortgage practices and the GSE's becoming the secondary market for crap mortgages. That created both the bubble, its inevitable collapse, and the speculation in derivatives.
Credit default swaps, in essence insurance policies against default, came into being because investors got a little nervous over these subprime mortgages.