The U.S. Congress has a long history of engagement on U.S. policy toward Sudan—since the end of apartheid in South Africa, there is no country in Africa on which Congress has focused more sustained attention. This bipartisan focus has been driven in part by diverse advocacy groups and public awareness campaigns on issues in Sudan ranging from famine to modern-day slavery, religious persecution, genocide, and other violations of human rights and humanitarian law. Terrorism concerns have overlapped the policy debates. Prior to the secession of South Sudan, Sudan was Africa's largest nation by area, and the site of its longest running civil war. In 2011, after decades of fighting broadly described as a conflict between the "Arab" Muslim north and "African" Christian and animist south, the country split in two. Mistrust between Sudan and South Sudan lingers, and unresolved disputes still threaten the stability of the region. The north-south split did not resolve other simmering Sudanese conflicts, notably in Darfur, Blue Nile, and Southern Kordofan (see Figure 1 ). Overlapping struggles between security forces and armed groups, among ethnic groups, and between nomadic and farming communities have caused extensive displacement and human suffering. Across the country, social tensions, economic pressures, and political dissent pose ongoing challenges for the Islamist government that came to power through a coup in 1989. The secession of South Sudan was a major financial blow to Sudan, which lost 75% of its oil production, two-thirds of its export earnings, and half of its fiscal revenues. The country carries a heavy external debt burden of $45 billion (78% of GDP), much of it in arrears. Khartoum's internal military operations against restive regions continue to draw international condemnation and have prevented Sudan from improving relations with many Western countries, including the United States. U.S. sanctions limit Sudan's access to U.S. dollars and, alongside debt arrears, impede Sudan's access to international financial markets and institutions. After the United States levied heavy fines against the French bank BNP Paribas in 2014 for violating U.S. sanctions against Sudan and other countries, most foreign banks stopped transacting with Sudanese banks, tightening the foreign exchange market and adversely affecting its trade. The International Monetary Fund anticipates that the breakdown in relations with correspondent banks could have a "considerable negative impact on the economy." The ongoing cost of waging war on multiple fronts compounds Sudan's economic troubles and, combined with allegations of political repression, fuels domestic criticism of the government and sparks periodic public protests. Relations between Sudan and key Arab Gulf countries, which have been important sources of trade, investment, and project financing for Khartoum, had cooled in recent years amid some Arab countries' concerns over Sudan's ties to Iran and its perceived support for the Muslim Brotherhood in other countries. Khartoum has since taken several conspicuous steps to address concerns about its relationship with Iran, including by expelling Iran's cultural attaché in September 2014 and closing its cultural centers in the country. The extent of its security association with Iran, however, remains subject to speculation. Iranian warships make routine port visits, and the two countries have a long history of diplomatic and military ties. Iran has reportedly played a significant role in the development of Sudan's military industry (Sudan now ranks as the third largest weapons manufacturer on the continent, after Egypt and South Africa). The two countries also reportedly have been involved in weapons smuggling to Gaza, and Israel has reportedly conducted several air strikes in Sudan to disrupt the route. Periodic allegations of Sudanese support for Islamist militias in neighboring Libya may also have contributed to strains in Sudan's relations with some countries, including Egypt. Many observers speculate that Sudan's decision in March 2015 to join the Saudi-led regional military intervention in Yemen, against Houthi rebels reportedly backed by Iran, may be motivated in part by an effort to reinvigorate Arab confidence and investment in Sudan. After Sudan gained independence from Anglo-Egyptian rule in 1956, successive governments in Khartoum perpetuated development disparities between the north and south that were, in part, a legacy of colonial administration. Northern "Arab"-led regimes espousing Islamist ideals have dominated Sudan's political history since independence, often pursuing policies to press distant provinces to conform to the political and sometimes sectarian priorities of the center, Khartoum, rather than accommodating the country's diverse local customs and institutions. Instead of forging a common national identity, these policies have exacerbated Sudan's racial, cultural, and religious differences. Government efforts to Arabize and Islamize the countryside met with resistance from southerners and other marginalized groups, sparking two related insurgencies in the south (1955-1972 and 1983-2005). Groups in other regions have risen up periodically, citing local grievances. In the 1980s, for example, minority groups in the ethnically diverse central states of Southern Kordofan and Blue Nile joined the southern rebellion, the Sudan People's Liberation Movement/Army (SPLM/A). Revenues from Sudan's oil reserves, which were discovered in 1978 in southern Sudan, primarily benefitted the north, in particular state elites in Khartoum. Oil money also financed the government's countering of domestic insurgencies with force—first in the south, and then also in the west and east. These counter-insurgency campaigns did not discriminate between fighters and civilians, and the government repeatedly questioned the neutrality of international aid agencies and restricted access to affected populations. The rebel groups persisted, and among them the SPLA was the most successful in gaining ground against the more heavily armed Sudanese military. The SPLA faced internal divisions in the 1990s, largely along ethnic lines; Khartoum fueled these splits by arming breakaway factions. Along the north-south border, Khartoum also used its oil revenues to finance local Arab militias as a front line against the south. Sudan's north-south war took a heavy toll on both sides, and in 2005, the government and the SPLM signed the Comprehensive Peace Agreement (CPA). The CPA enshrined the south's right to self-determination after an "interim period" of more than six years, during which the SPLM and the ruling National Congress Party (NCP) formed a unity government. Despite the NCP's stated effort to "make unity attractive" to southern Sudanese during the interim period, southerners saw few, if any, benefits from remaining part of Sudan and voted overwhelmingly in a January 2011 referendum to secede. South Sudan achieved independence in July of that year. The CPA failed to resolve several contentious issues, and talks have continued on border disputes and related security issues, debts, and once-shared resources, such as oil. Sudan and South Sudan signed partial deals on security and economic cooperation in 2012, but the full deployment of a joint monitoring mission to ensure the demilitarization of the border has been repeatedly delayed and is limited to sporadic aerial surveillance. The proximity to the border of rebel activity in Sudan's "new south" (Southern Kordofan, Blue Nile, and the southern part of Darfur) and the unresolved status of contested areas such as the Abyei region complicates border demilitarization. The border region of Abyei, which was accorded special semi-autonomous status in the CPA, has repeatedly been a flashpoint for violence. The deployment of the U.N. Interim Force for Abyei (UNISFA) defused a violent standoff in 2011 between Sudan and South Sudan, but tensions among local communities still have the potential to destabilize the border and draw the two countries back into direct conflict. Under the CPA, Abyei residents were to vote in a 2011 referendum on whether the area should retain its special status in Sudan or join South Sudan. A dispute about voter eligibility has delayed the process. The Ngok Dinka, who have historically comprised a majority of the area's permanent residents, controversially held their own referendum in 2013, voting to secede from Sudan. Neither Sudan nor the international community has recognized the result. The final status of Abyei is likely to remain unresolved until Sudan and South Sudan negotiate a resolution, possibly as part of a broader deal on outstanding issues between the countries. The United Nations has pressed, unsuccessfully to date, for the establishment of a temporary local administration and police service to maintain order until a final settlement is reached. The armed forces of Sudan and South Sudan have engaged in minor clashes along the border sporadically since separation, most prominently in 2012 when the South Sudanese army briefly occupied the Sudanese oil town of Heglig, purportedly acting in self-defense after an attack on its territory. Sudan bombed one of South Sudan's oil fields in retaliation and further skirmishes ensued. South Sudan periodically accuses Sudan of conducting other air strikes inside its territory. Sudan alleges that South Sudan's ruling party, the SPLM (the former rebel movement), provides support and refuge for Sudanese rebel groups (the likely target of reported air strikes). South Sudan contends that Sudan has, at times, provided weapons and other support for South Sudanese rebel militia, including, most recently, the rebellion known as the SPLM-in Opposition (SPLM-iO), led by South Sudan's former vice president, Riek Machar. In the context of South Sudan's current conflict, there is concern that this alleged proxy support by both sides could spark a wider regional war. Given the mass displacement already caused by the conflicts in the two countries, direct hostilities between the two countries could have devastating humanitarian consequences. The CPA did not resolve Sudan's long-standing center-periphery tensions. Khartoum has continued to respond to the political demands of restive regions more often with force than reform.