This spread is widely followed worldwide as any number below or close to 0 tends to indicate impending slowdown in the US Economy, (which is the world's largest) and thus the most important.
You will notice that the Yield Curve tends to cycle and that the initial low point, marked as Point 1, was in 1989; when the US Economy suffered a total collapse in domestic manufacturing and started to initiate the concept of outsourcing manufacturing, particularly semiconductor fabrication to Taiwan, heavy shipbuilding to South Korea and automobiles and domestic electronics to Japan.
The fall of the Berlin Wall in 1990, which was joyfully called the "End of History" was when US Corporations found themselves in the unique situation of no longer having to give in to their workers demands for unionization and normal humane conditions; in order to pacify them and have them stop demanding the same work and social security conditions of their fellow workers within the Soviet system meant a boom till 1992. Those workers did not have a leg to stand on from 1990 onwards.
Point 2 is the dot.com crash of 2000, Point 3 is the Great Financial Crisis or GFC and the collapse of the Mortgage Backed Security or MBS global housing market in 2006/07.
These two events were frantic attempts to keep the US Reserve Currency system afloat as well as to inflate the US Stock Markets and keep failing corporations commercially viable. This was achieved by the total and absolute destruction of Iraqi Society and subsequently the total annihilation of Libya as a functioning sovereign nation, in order to keep the Petro-Dollar system concurrent.
We are now approaching Point 4, which is a Currency Crisis and a collapse in the US Dollar or the USDX or DXY . This will lead to a massive convergence towards digital currencies and IMF/World Bank sponsored attempts to replace fiat. The question remains; will the debt burden of those same workers within capitalism be written off and if so, will that be initiated via a Bernie Sanders led Administration in the US before the situation gets totally out of hand.
With that in mind, I have included the Weekly SPX Chart below with the corresponding falls after Curve Inversion marked in.
There is a huge spike in the RSI during Jan18 but the Yield Curve had not inverted. The fall in the SPX with the RSI at a min during Dec19 is a technical correction, unrelated to Yield Curve Inversion.
Also you will notice that as the Curve Inverts, the MACD Structure begins to slide towards 0 and below, with a final trough at the SPX Index low itself.
So putting the Curve Inversion in context with the falling MACD Struct and the RSI peaking, seems to provide and early indication of an Index Correction.
You will notice the 21st Oct Vix Expiry at 20.55 which is far higher than the Vix quotes prior to Oct as well as higher than the Nov Fix.
The important US Elections conclude in November. Is the market indicating some sort of unexpected outcome.