defaulted debt purchases. By 2006, "new issues rated CCC to CCC- were at an all time high of $20.1 billion". Other buyers include brokerage firms, mutual funds, private equity firms and specialized debt funds such as collateralized loan obligations. The United States has the most developed market for distressed securities. The international market, especially in Europe, has become more active in recent years as the amount of leveraged lending has increased, capital standards for banks have become more stringent, the accounting treatment of non-performing loans has been standardized, and insolvency laws have been modernized. Typically, the investors in distressed securities must make an assessment not only of the issuer's ability to improve its operations, but also whether or not the restructuring process (which frequently requires court supervision) will benefit one class of securities more than another. Sovereign debt In 2003, Seveq observed that the emergence of the secondary debt market led to a "modern sovereign debt litigation" and the creation of an industry of "professional suers of foreign states". In a 2010 article, Blackman and Mukhi examined a series of litigations employed by distressed funds investors in their lawsuits against defaulted sovereign states. The business plan involved buying the sovereign debt instruments at a deep discount based on a very high risk, and then attempting to enforce the full claim. The strategy is most effective when the sovereign state lacks bankruptcy protection. These investors however are constrained by "the sovereign-immunity rules that national legislatures have enacted and national courts have elaborated" to protect the vulnerable nation states from litigation. While private debtors have the resource of bankruptcy protection, sovereign states do not. There have been "sporadic calls for a bankruptcy analogue for sovereign states" similar to the bankruptcy process for private debtors, however these calls have lacked momentum. According to the African Development Bank Group, at least twenty heavily indebted poor countries in Africa have been threatened with or subjected to legal actions by commercial creditors and hedge funds since 1999. Zambia In 1999, the US firm Donegal International purchased $40 million of Zambian debt owed to Romania for the "discounted purchase price" of $3.2 million. In 2007, a British high court granted the company "permission to enforce a claim for tens of millions of dollars against the Government of Zambia". Liberia In 2009, a British court awarded $20 million to hedge funds suing Liberia. Before the hedge funds could