When I look back at history, it seems like major economic turmoil is very often followed by outbreaks of major warfare or at the very least significant flirtations with major conflict. The Great Depression was followed by WWII, the decline toward the end of the 60s by the hottest period of Vietnam, the dot.com crash by 9/11 and Iraq, and the 2008 crash by the Ukraine crisis and what seems to have been a near miss between the USA, Russia, and possibly other powers. 2008 was also followed fairly shortly by the rise of ISIS and a re-heating of Iraq and its general region.
We're hearing a lot about an impending emerging market debt crisis, and we know China has gone to 'heroic' efforts to backstop its stock market and real estate markets against the first stages of what appeared to be an unfolding crash. It's entirely possible that another economic crisis is brewing in China and other 'emerging' markets, and it could be a bad one. If that's the case at some point it will exceed the ability of even China's autocracy to prevent it with currency and market manipulations.
As I led off with above, I doubt that there's an overt decision that happens. I doubt anyone says 'well, the economy's down so we better have a war!' Instead I suspect it's a bit like tectonic plates. When an economic crash happens it exacerbates stresses that are already present in the system and quite likely pushes some people and/or state actors over the edge. People often behave more desperately and irrationally under economic stress; you can see this in the willingness of former Soviet officials to actually distribute such deadly material during the waning days of the USSR. Not being able to eat is a powerful motivator.
Edit: not deleting this, but I hate to have posted it hours before hearing about Paris.