Forty percent of the world's economy is already in recession. When a boom collapses, it can turn every country against the other. There is too much capacity for too few consumers. Someone has to close a lot of plants and lay off a lot of workers. Countries lower their currencies to make their products cheaper.
Companies merge, purge and export jobs rather than goods abroad.
People start demanding that their government act to protect them. Malaysia just cut off currency exchange. Russia defaulted on short term bonds. Thailand and others saw their currencies plummet behind fleeing capital. Japan has been frozen, unable to move.