United States why the issue of debt have a significant impact on the global financial markets?

United States of huge debt problem first began Yu World War II period, and real on global economic constitute threat is from 1971 Shi any United States President Nixon announced gave up gold standard business began of, dollars and gold decoupling, floating system established, United States began implemented so-called "debt economic mode", that in global economic integration, and bulk commodity price to dollars for pricing and settlement units of premise Xia, United States must keep trade deficit.
This is for the purchase of commodities of other countries and the only way to get dollars, after the States get $, and through the purchase of United States Government debt back United States native, did so because United States bonds credit liquidity and profitability than other financial products also can hold large amounts of capital. In fact, United States debt is US dollar hegemony of subsidiary products! As long as hegemony of dollar in debt crises will repeatedly attack.
from the top United States debt in real terms, debt problem is not just United States their own problems, its every move also involves the flow of global capital and liquidity problems in the financial markets. Therefore, after the debt crisis erupted, and often trigger global turbulence in the financial markets. In May 2011, for example, United States Government debt amounted to United States Congress to allow the 14.29 trillion dollar limit, if you don't raise the debt ceiling or spending cuts, it will begin to default on its debt, unable to pay United States bond principal and interest on the United States will default on its debt. Once a breach occurs, then the United States will definitely downgrade the sovereign debt ratings, holding us debt of countries and individuals will suffer losses, caused the Treasury selling, which further caused turmoil in financial markets.
in August 2011, one of the three major international rating agency, standard and poor's downgrade of United States sovereign credit rating, AAA up to below AA +, Outlook negative. This caused further panic in the market, major stock markets around the world fell sharply, rise in risk aversion, rising precious metals such as gold and silver benefit. Similar scenarios have appeared in 2013.
in February 2014, the United States Congress to unconditionally was adopted by 55 votes to 43 in the Senate Bill to raise the federal debt ceiling until March 15, 2015. At that time, the United States public debt at around 17 trillion dollars, raise the debt ceiling Bill comes into effect, United States Federal Government to raise debt limit before March 15, 2015. Implementation of the Bill temporarily mask the United States debt problems, but this is only a short-term expedient.
from the latest data, end of November 2014, United States total public debt hit a record high, above $ 18 trillion for the first time, reaching $ 18.005 trillion. According to the latest data, released on September 30, United States in 2014-nominal gross domestic product (GDP) of approximately US $ 17.555 trillion, that is, United States total public debt to nominal GDP ratio once again break through 100%, at 103%.
three major international rating agencies found that United States Government bond 3-a precondition is that GDP proportion of total debt of no more than 110%, this means that if the United States Treasury to continue at the current rate of increase, then very likely to suffer credit rating downgrades. This likely to reignite the turmoil in global capital markets. In addition, on March 15, the United States raising the debt ceiling Bill coming due, debt problems back into the world of the view of investors, in my opinion, this will become an important cause of US dollars in the first quarter fell.