
World's GDP (or total global economic activities) per year is about USD60 trillions in Y2008. US GDP accounts for USD13 trillions (about 22%). Due to the US multiplier effect of about 4, a growth rate of 1% by US will increase US by 4% or world's GDP by at about 1% but vice-versa, a US drop of 1% will decrease global GDP by 1%.
US total debt to-date is about USD45 trillions; Corporate debt is USD18 trillions, Govt (or national) debt is USD11 trillions, and Personal debt is USD16 trillions.(11 trillion of mortgages, 4 trillion of credit card, 1 trillions of others). Of the three, the personal debt is of most concern.
Corporate debt is considered a form of capital investment and working capital. Given the USD18 trillions corporate borrowings to the annual activities of USD13 trillions, most analysts would consider the ratio of 1.38 times as very effective capital usage where the payback shouldn't be of any concern. The Corporate USA should be self financing as its projected future earnings is expected to pay for itself. The low capital utilization is due to US high service sector component of the economy.
As for national debt, it is assumed that most of the borrowings were used for infrastructure development which is also considered a capital investment too. US govt expenditure is an exception as a sizable portion of the infrastructure development is not paid by the US government. US govt spent most of its money on wars and its war machinery, health care and some basic education expenses and as such, a sizeable national debt are for consumption and not capital investment. The US baby boomers' generation is going into retirement and with the increasing demand on health care, which in turns will put further pressure on US national debt.
The total US personal debt of USD16 trillions without any savings poses the biggest hurdle to the return of normal economic cycle as US' individuals would not be able to sustain itself and repay its debt. Though USD600 billions have been written off, it is still far from over. The recent financial seizure is just the beginning of the spiraling downward of credit crunch. Now, there is hardly any interbank loaning activities. The US banks are cutting back of normal business loans to businesses (or companies) and also to individuals. This will leads to companies cutting back on employment which will result in sizable unemployment. Unemployment and lower personal loans availability will feed into fall of consumption which will further cause the drop of businesses and further cut back of employment. As such, companies' profits will be badly hit which causes the big drop of US share prices. This vicious cycle will not only affects US economy, but the world's economy as US is the largest consumers' nation.
In 1931 where US has 300% debt against its GDP, the economy simply collapse, resulting in the 1st Great Depression. At that time, there was global contagion, resulting in the collapse of the global economies, one after another which resulted in the 2nd World War.
Today, US has 350% debt, though with the benefit of advance economic and management theories, US will enter into a severe recession, but the bigger concern is will US drag the world's economy into the 2nd Great Depression?