The world economy recovered after a decade-old financial crisis, but 2018 diminished optimism among bankers and economists: they are increasingly nervous and less likely to believe in the sustainability of this recovery.

The first clear and vivid illustration of their concern could be the collapse of the stock market - the most sensitive barometer of the world economy..

Only one question - how soon will it happen.

The current stock market boom is the longest in history; it has been going on for nine years now..

Now everything seems to be in order, the world economy is growing, the financial system is stable. However, investors are noticeably nervous: clouds are gathering on the horizon, and problems are not far off, they are sure. On BBC News, we understood the reasons for their fears and identified four main.

Money is becoming more expensive The world has recovered from the last depression of a decade ago, employment and the economy are growing, and with them - people's incomes and prices. To prevent this from turning into high inflation and not become a threat to financial stability, central banks in leading countries are raising interest rates.

As a result, loans become more expensive, companies spend more on debt servicing, profitability decreases, and with it profit.. As a result, companies return less money to shareholders through stock repurchases and dividends.. The growth prospects of their business are growing dim, those who want to buy a share in it in the form of shares become noticeably less, and sell - more and more.

However, the period of cheap money has come to an end, and investors have doubts that the business growth rates of companies - from leaders of the new economy like Apple and Amazon to traditional giants like Visa and Coca-Cola - will be the same and not slow down..

And since the rates are rising, investors again have a decent profitable alternative to risky investments in stocks - US government bonds, bringing more than 3% per annum with zero risk..

The world is not ready for a new crisis. Bankers and economists do not believe that recovery is stable, and they fear that the new crisis is not far off..

"Part of it reminds me a little of 2006. It seems that everything is fine, - said the head of the British bank Barclays Jess Staley. “Even with problems like Brexit or the political situation in the United States, the economy is growing, unemployment is at an all-time low.”.

“But I’m sure it’s time to start worrying,” said Staley, who watched from the first row of the past crisis: in the days of the collapse of Lehman Brothers, the American investment bank, he worked as the top manager of his main competitor, J. Morgan.

The world economy is cyclical - periods of growth are replaced by crises and depressions. Economists cannot yet unequivocally answer the question of what politicians should do in order for nations to become rich.

After each crisis, the world draws conclusions on what went wrong and tries to fix the problem.. But every time everything is repeated with a new force..

Partly because structural changes turn out to be half-hearted due to social and political inertia — the upper classes cannot, and the lower classes do not want. Partly because progress introduces new unknowns.

It happened this time too.. In response to the large-scale crisis of 2008–2009, caused by banks' creative approach to credit risks, the authorities of the largest economies responded no less creatively.. They pumped the economy with cheap money and saved the banking system at the expense of taxpayers, while at the same time increasing capital requirements and supervision.

This turned into a huge jump in public debt and an unprecedented reduction in loan rates to zero and even negative.

After such stimulation, the world economy recovered and gradually returned to growth.. Now the time has come to curb the incentives, but structural distortions have once again been eliminated only partially, and new problems have been added to them: from the dominance of Internet giants to trade wars and the rise of populism..

In addition, record debts and extremely low rates deprived the government of the tools to deal with the new crisis, should it happen today. And the reasons to expect it.

The growth of the world economy is under threat. Over the past few months, the world has brought so many unpleasant surprises that the International Monetary Fund has worsened its forecasts for the first time in two years - in April he expected the global economy to grow by 3.9% in the current and next years, and in October decided that more than 3.7% per year will not work.

Considering the fact that last year the size of the world economy exceeded 80 trillion dollars, a revision of 0.2% means that the world will miss about 160 billion dollars a year - this is more than the annual GDP of Ukraine or Kazakhstan.

The main threats are political. Since one of the reasons for the crisis was gigantic public debt, especially in the eurozone, for the next decade, to eliminate this skewing of the government, spending was cut, which led to increased unemployment, stagnation of household incomes and the widening of the gap between rich and poor..

The discontent resulted in the rise of political and economic nationalism, vivid manifestations of which were Britain’s decision to leave the EU and the election of Donald Trump as US President.

Trump started trade wars on all fronts, choosing China as the main target, and set about breaking the entire system of international cooperation - from the World Trade Organization and NATO to an agreement on combating climate change and a nuclear deal with Iran..

Meanwhile, in the Old World, the problems of the eurozone were added to Brexit: from the victory of populists in Italy to the rise of the Right and the end of the era of Angels Merkel in Germany.

Isolationism not only undermines global economic growth, but also reduces the likelihood of a coordinated response to the next crisis, as was the case last time when leading economies agreed on joint actions..

"Trade reflects what is happening in politics, and with it the situation is unstable in a number of countries, which creates new threats," wrote IMF senior economist Maurice Obstfeld in October..

“In addition, in many key economies, growth is ensured by the actions of the authorities, whose maintenance in the long term is impossible,” he writes and urges politicians to come to their senses and carry out structural reforms while they have money.. “Despite the narrowing of the political space in some countries, which makes it difficult to make balanced decisions, now is the right time for positive action than ever”.

Reporting season Rates, distortions and economics are an important background for a business, but there is no better reason to sell or buy a stake in it than the results and forecasts of the companies themselves.. Those who raised capital in the market by selling shares are obliged to report to shareholders once a quarter - and now is the time.

As the market’s nerves are at their limits, any slip or pessimistic forecast of a large company may cause a sell-off.. And the reasons for this are enough.

First, the rising rates mentioned above gradually begin to affect profitability..

Secondly, trade wars threaten cost increases due to duties and scrapping of cross-border technological chains, primarily Sino-US.

Thirdly, the effect of Trump's tax reform is fading away, and as a result, company reports no longer show the growth in income that was in the first months thanks to benefits..

Fourthly, technology giants like Facebook, Apple, Google and Amazon have been the growth leaders in the stock market in recent years.. Belief in their ability to grow at the same pace of revenue and profits is gradually melting, and investors are waiting for the right moment to take profits and step aside to wait out the coming period of uncertainty in a safe haven of cash, gold and US government bonds..

And fifth, the steady growth of the American economy and rates in the context of a sluggish recovery in the world and the instability of emerging markets leads to the fact that the demand for American assets is growing - and with it the dollar. As a result, overseas earnings of US companies fall when converting to dollars, and their products become more expensive in other currencies and lose competitiveness..

Those who manage the money of investors in the market, hope that this time will carry.

"If we rise above the fray and look at the big picture, we will see that yes, economic growth has slowed down a bit compared to the peak values, but it is still confident that interest rates are rising, but have not yet reached the level that holds back the economic growth, inflation accelerates, but remains under control, "says Monique Wong of the investment company Coutts.

“So I think this is a correction within the bull market. There is nothing unusual about these corrections, and they are also useful. ".