The strangling symbiosis-
The US economy, due to overpriced US$ became in the last 20 years the vacuum cleaner of the world excess production capacity, and payed for it with borrowed money. The same happened in Europe in much smaller scale between the northern producing (mainly Germany)and the southern borrowing and consuming countries. This imbalance had to bring economic crisis, unless some politician would stop this trend before the crisis. It of course did not happened. Democratically elected politicians make decisions that in short term make them very unpopular only when they are forced to do it under threat of economic crisis.
The last economic crisis is relatively mild compared to the 1929 economic crisis only because of the responsible economic policy of China, which in-spite of common understanding that US will never eventually pay back its debt in the real terms, agreed to continue their policy of lending to US and gradually reducing the mutual dependance of Chinese and US economy. Stable economic growth can start again only after the US debt problem will be solved.