Most of what goes on in the stock markets these days has to do with what the markets expect the federal reserve to do. The fed was acting as if rate hikes were coming and There will be no More QE due to a supposed recovery. That alone was enough to shake things up and make the markets go down. I highly doubt the Fed will actually hike rates meanwhile the market crashes.. I expect them to return to more QE and low interest rates. Flooding the market with easy money may very well prop things up all over again..but how long that will continue to work, there's really no way of knowing.