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Puerto Rico defaulted on its $58 million debt repayment this week for the first time in its history. With its failure to repay creditors, the commonwealth joins the ranks of countries and governments burdened by crippling debt levels and extremely low credit ratings.

Moody's Investors' Service rates seven countries Caa1 or worse, several tiers lower than Ba1, which still carries a significant credit risk. These countries are approaching or have narrowly escaped bankruptcy. Ukraine is rated Ca, which is currently the lowest credit rating of any country reviewed by Moody's.

All seven national economies instill relatively little confidence among investors. However, Jamaica's credit rating was upgraded by Moody's this year, and Argentina's and Belize's credit ratings remained stable. The remaining four countries, on the other hand, were downgraded.

A country's history of fiscal responsibility, including past defaults, and current compliance with IMF debt repayment plans, are major contributors to Moody's evaluations.

Extremely high debt levels, which while not always a feature of unhealthy economies, can also contribute to a country's poor credit rating. The debt of four of the seven countries was equal to more than 75% of GDP. In Jamaica and Greece, debt was well over 100% of GDP.

Political conflicts have also weakened some of these economies, which in turn has introduced more uncertainty and increased risk. Ukraine's conflict with Russia over its annexation of Crimea, for example, and the resulting U.S. and European sanctions, have contributed to the country's downgrade in March.

Borrowing funds in the international bond market is often far more costly for countries with poor credit ratings. Investors require greater returns on what they perceive to be riskier investments and charge higher interest rates as a result. For example, a 10-year U.S. Treasury Note has an annual yield of just 2.16%. By contrast, a comparable bond recently issued by Jamaica pays out 6.44% a year. Yields on 10-year Greek government bonds reached 29% in early 2012, just before the country defaulted.

Foreign investment is vital for most countries, particularly developing nations. To promote interest among investors, countries use a range of strategies. Often, these countries issue bonds in other, safer currencies in order to be more competitive in the international bond markets. Nations such as Argentina, Jamaica, Belize, and Ukraine have all issued bonds in other nations' currencies. Inflation rates for common currencies such as the dollar, yen, and euro are typically far lower and more stable than the currencies of the issuing countries. This means that investors do not need to worry as much about their investment losing value.

Based on credit ratings provided by Moody's Investors Service, 24/7 Wall St. reviewed the seven countries with credit ratings of Caa1 or worse. A rating of this level indicates considerable credit risk. Because many of these nations have significant debt in other currencies or have otherwise weak currencies, we used foreign currency ratings and outlooks for these nations. Figures on GDP growth, inflation, unemployment, population and debt levels are estimates for 2014 from the IMF's World Economic Outlook.

These are the 7 countries at risk of default.

7. Belarus

> Moody's credit rating: Caa1
> Moody's outlook: Negative
> 2015 Gov't debt (pct. of GDP): 39.6%
> 2015 GDP per capita (PPP): $17,836

Considered by many to be the last dictator in Europe, President Alexander Lukashenko has ruled Belarus since 1994. Part of Lukashenko's reputation likely stems from his refusal to privatise state enterprises, which has discouraged foreign investment, according to the BBC.

Like several other Commonwealth of Independent States (CIS), Belarus's economy — and its credit rating — is largely dependent on the Russian economy. U.S. and European-imposed sanctions on Russia following the crisis in Ukraine, as well as falling oil prices in recent years, are among the major contributors to the weakening confidence in Belarus's economy. In an attempt to counteract rampant inflation, Belarus tied its ruble to three foreign currencies in January: 40% Russian ruble, 30% U.S. dollars, and 30% euros.

Moody's in April downgraded Belarus's sovereign debt rating to Caa1 from B3 — Belarus is one of only seven countries with a credit rating worse than B. Ratings C and worse are associated with relatively high levels of uncertainty, and creditors can expect a 90% to 95% recovery rate — the expected percentage of principal and interest returned to lenders — in countries with Caa1 ratings.

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6. Argentina

> Moody's credit rating: Caa1
> Moody's outlook: Negative
> 2015 Gov't debt (pct. of GDP): 49.5%
> 2015 GDP per capita (PPP): $22,459

Argentina's current fiscal woes can be tied back to the late-1980s. In 1989, The New York Times reported that inflation in the South American country was estimated at an annual rate of 12,000%. In an attempt to tame the country's hyperinflation, the government tied its currency, the peso, to the U.S. dollar. While the peg had the desired effect and attracted foreign capital, it also hindered the Argentinian government's ability to counteract currency appreciations that made its exports more expensive relative to the rest of the world. Rather than abandon the peg, Argentina cut wages, which helped tame inflation but also drove unemployment up and tax receipts down. In 2001, Argentina defaulted on roughly $100 billion worth of debt.

While most of the nation's bondholders at the time agreed to debt restructuring deals, a few investors refused. After a U.S. court ruled in 2012 that Argentina could not pay its current bondholders without paying the holdouts as well, the country was forced to default in August, 2014. With elections this October, many presidential candidates are outlining their plans to revitalize Argentina's economy by tightening monetary and fiscal policy as well as looking to the international community to finance its debt.

5. Jamaica

> Moody's credit rating: Caa2
> Moody's outlook: Positive
> 2015 Gov't debt (pct. of GDP): 132.8%
> 2015 GDP per capita (PPP): $8,784

While Jamaica's credit rating of Caa2 is among the worst, it is a recent upgrade from a Caa3 rating. Moody's also upgraded the country's outlook to positive in May. No other country with such a poor rating has a positive outlook. Jamaica recently simplified its tax return filings, reformed tax incentives, and implemented a minimum business tax. According to Moody's, the improved business climate supports private investment and confidence in the economy.

Still, Jamaica's consistently high debt burden, coupled with high interest rates, have weakened the credit rating. Sovereign debt remained above 140% of GDP each year from 2009 through 2014, when it was third highest compared to other countries. Government debt fell slightly this year to an estimated 133% of GDP. However, this was still higher than all but three other countries.

4. Belize

> Moody's credit rating: Caa2
> Moody's outlook: Stable
> 2015 Gov't debt (pct. of GDP): 75.7%
> 2015 GDP per capita (PPP): $8,321

A small country in Central America, Belize is home to just over 360,000 people. It is one of the smallest economies in the world with a GDP of $1.8 billion. Borrowing heavily for infrastructure projects, Belize accumulated a total debt of over $540 million. In August 2012, the country's central bank announced that it would not be able to make a $23 million bond payment. Due to concerns surrounding the impending debt restructuring, Moody's downgraded the country's government bond rating to Caa1 from B3 in early 2012. It was later downgraded further to Ca only to be upgraded back to Caa2 in April 2013, after terms of the debt restructuring were agreed upon. Belize's Credit rating has remained stable at Caa2 since April 2013.

3. Venezuela

> Moody's credit rating: Caa3
> Moody's outlook: Stable
> 2015 Gov't debt (pct. of GDP): 39.6%
> 2015 GDP per capita (PPP): $16,346

Between September 2014 and January 2015, all three major credit rating companies downgraded Venezuela's credit. Moody's cited plummeting fuel prices as the primary factor in the downgrade. Nearly 94% of Venezuela's export earnings come from oil. Consequently, the country's risk of default increases substantially as fuel prices drop. Crude oil went from an average of $88.42 a barrel throughout 2014 to a mere $54.03 a barrel in December of 2014. Moody's predicts that Venezuela's account balance will shift from a 2% surplus of GDP in 2014 to a deficit of 2% of GDP in 2015. Despite the series of downgrades, Central Bank President Nelson Merentes expressed optimism that the Venezuelan economy would grow in 2015.

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2. Greece

> Moody's credit rating: Caa3
> Moody's outlook: Rating Under Review> 2015 Gov't debt (pct. of GDP): 172.7%
> 2015 GDP per capita (PPP): $26,773

Greece was among the countries hardest-hit by the 2008 global financial crisis, and the country eventually received several large bailouts totalling 240 billion euros. Greece defaulted on $138 billion of its debt in 2012, the largest sovereign default ever recorded. Debt restructuring following the default and a return to the international bond market last year were hopeful signs of economic recovery. However, the debt restructuring accompanied severe austerity measures at a time of already grim financial hardships for many Greek residents. Since 2012, the estimated unemployment rate in Greece has remained between 24% and 25%, among the highest in the world.

This January, Greece once again returned to the international spotlight after Greek voters elected the left-wing party Syriza, which would form the eurozone's first anti-austerity government. Greece's finance minister under Syriza, Yanis Varoufakis, supported a stubborn rejection of the terms offered by the troika: the European Union, the European Central Bank, and the IMF. In a historic referendum in July, a majority of Greeks voted "no" to spending cuts and tax increases demanded by repayment plans. Varoufakis resigned after only six months, however, and Greece's new finance minister, Euclid Tsakalotos, insists that "Greece is committed to honor its financial obligations to all of its creditors in a full and timely manner."

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1. Ukraine

> Moody's credit rating: Ca
> Moody's outlook: Negative
> 2015 Gov't debt (pct. of GDP): 94.1%
> 2015 GDP per capita (PPP): $8,278

Ukraine's conflict with Russia over its annexation of Crimea continues to fuel the country's financial problems. While the IMF approved Ukraine's debt restructuring plan in March, Ukraine has the worst credit rating of any country reviewed, downgraded this year from Caa3 to Ca, the second lowest possible level. Creditors can expect a 35% to 65% recovery rate on loans issued by the country. According to Moody's, "The likelihood of a distressed exchange, and hence a default on government debt taking place, is virtually 100%."

The same day that Moody's issued the downgrade, the National Bank of Ukraine announced the establishment of the Financial Stability Council. According to Governor of the National Bank of Ukraine Valeriia Gonatreva, the Council's function will be to "take a comprehensive and systemic approach to identify and mitigate the risks threatening the stability of the banking and financial systems of the country."

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