Why are yield curves so flat?

The very flat yield curves in the recent period (in the United States, the euro zone and Japan) can have several origins: Low expected inflation; Forward guidance: central banks commit to keeping short-term interest rates low; The disappearance of term risk premia (linked to the variability of long-term interest rates); The disappearance of sovereign risk premia (linked to the risk of fiscal insolvency for governments), due in particular to the insurance against the risk of government defaults provided by central banks. Econometric analysis shows that the slope of the yield curve depends on: In the United States and the euro zone, expected inflation and the sovereign risk premium; In Japan, the sovereign risk premium and forward guidance.