Economically, the 11 years since the Global Financial Crisis of 2008-09 have been one relatively coherent era of modest growth, rising wealth/income inequality and coordinated central bank stimulus every time a crisis threatened to disrupt the domestic or global economy.
This era will draw to a close in 2020 and a new era of destabilization and uncertainty begins.
Why will all the policies that have worked so well for 11 years stop working in 2020?
All the monetary/fiscal policies of the past decade were simply extreme versions of tried-and-true policies that central banks and governments have used for the past 75 years to restore growth in a recession or financial crisis: lower interest rates, increase credit/liquidity, and ramp up government spending (i.e. deficit spending) to compensate for declining private-sector spending.
These policies were designed to be short-term stimulus programs to jump-start the economy out of a slowdown (recession), which typically lasted between 9 and 18 months.
These policies are now permanent, as the system is now dependent on these policies. Any reduction in central bank stimulus causes a market crash (witness the 20% drop in 2018 as the Fed slowly raised interest rates from near-zero) and any reduction in deficit spending threatens to trigger a recession.
The problem is that these policies create distortions that cannot be fixed with more of what caused the distortions in the first place: more extreme monetary and fiscal stimulus.