Business Insider reached out to the brightest minds on Wall Street to get their thoughts on what just happened.
Hopefully, they'll help us get a better handle on what is about to happen in 2016.
Charlene Chu, of Autonomous Research, is widely considered one of the most brilliant China analysts in the world.
So we asked her to send us a chart that helped her make sense of the world in 2015. Naturally it's about China.
"The chart below highlights the growth problem China is grappling with. In our view, a broken growth model lies at the core of China's financial sector issues," she wrote in an email to Business Insider.
"This chart comes directly from official data, which is not adjusted in any way. Secondary industry comprises about 40-45% of GDP. As the title says, nearly half of China's economy is already experiencing a very hard landing. This will likely intensify in 2016, which will weigh on global growth and add to corporate debt repayment problems."
CEIC and the National Bureau of Statistics; Charlene Chu, Autonomous Research
In China, GDP is classified into three industries, primary (agriculture), secondary (manufacturing and construction), and tertiary (services).
This slow down in the secondary industry is part of China's intentional shift toward an economy focused on services and consumer consumption, rather than manufacturing.
Chu's point is that it's happening harder and faster than anyone thought it would.
All of this became all too apparent in 2015. This year China experienced two mainland stock market crashes, it devalued its currency, and once booming sectors of the economy - like exports and property - slowed sharply.
In response, the government loosened monetary policy and enacted stimulus measures. The measures have had a limited impact, however, indicating that more structural measures will be needed to remedy the situation.
Chu expects this slow down to continue through 2016, impacting markets around the world.