The euro, which only began in 1999, isn't long for this world, says Jeremy Warner, assistant editor of The Daily Telegraph.

"Misconceived from the outset as a monetary union unsupported by shared political and fiscal arrangements, the euro has always been a deeply flawed endeavor," he writes.

And what's going to kill off the currency?

"Not the financial traumas that first threatened its existence, but political contagion, with the single currency paradoxically spawning exactly the same kind of resurgent nationalism, popular anger and political instability it was designed to eradicate."

The euro has stabilized in recent weeks after Greece's European creditors agreed to another bailout. But the global economy is at risk, Warner says. "If the global economy is indeed about to enter another downturn, then we can expect the eurozone crisis to resume quite quickly in some shape or form."

China's economic growth is slipping, Japan's economy contracted in the second quarter, and the eurozone grew just 1.3 percent then.

"To survive, the eurozone desperately needs a recovering world economy," Warner says.

Ruchir Sharma, head of emerging markets and global macro at Morgan Stanley Investment Management, is worried about the world economy too. China's woes may send it over the edge, he says.

"Over the past 50 years there has been a global recession once every eight years, on average, so the next one may be brewing," Sharma writes in The Wall Street Journal.

"The policy panic in Beijing over its currency and the fall of its stock market suggest that the next global recession likely will be 'made in China.'"

The Shanghai Stock Index has dropped 27 percent since June 12, and the yuan has slid 3 percent since China's government devalued it last week. The economy officially grew 7 percent in the second quarter, but analysts say the true figure is closer to 3-5 percent

The U.S. economy used to be the prime cause of global recessions. But since 2010, China has accounted for one-third of global growth, compared to 17 percent for the U.S., Sharma explains.

"The world is one shock away from recession," he writes. "A debt-laden China is now the critical link, and another one- or two-percentage point decline in its growth rate could provide that shock."

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