The people of Zanzibar go to the polls on March 20 to choose a new president and government for the second time in five months. The previous election was annulled three days after the vote, in what was widely seen as a move by elements within the ruling Chama Cha Mapinduzi (CCM) to prevent an imminent opposition victory. The opposition Civic United Front (CUF) will boycott the election rerun. The Tanzanian government has deployed military vehicles and personnel to the quasi-autonomous archipelago amid fears of an escalation of violence. The latest developments should come as no surprise, given the history of election controversies on the islands.

Zanzibar has a long history of controversial, closely fought, violent elections. The Zanzibar Electoral Commission (ZEC) has played a critical role in sustaining the CCM, the ruling party in both Zanzibar and on the mainland, in power. In 1995, for example, international observers found evidence that CUF leader Seif Sharif Hamad was denied victory due to rigging by the ZEC. The aftermath of disputed elections in 2000 led to the army and police allegedly killing 35 protestors and injuring 600 others. Officials and militia from the CCM went on a house-to-house rampage, arresting and abusing suspected opposition supporters, prompting some 2,000 people to flee to Kenya. The nullification of the results of this year’s election by chairman of the ZEC Jecha Salim Jecha on October 28, following the declaration of 31 of Zanzibar’s 54 constituencies, suggests that nothing has changed.

The international community failed to pay close attention to the situation in Zanzibar in the run-up to the elections, mistakenly thinking that the Government of National Unity formed in 2010 between the two parties was a guarantee that the October 2015 elections would not be problematic. This was wishful thinking. In addition to the historic tensions between the two main islands of the Zanzibar Archipelago—Pemba and Unguja—three additional factors have increased the political temperature. The first is the ongoing debate about Tanzania’s new constitution. The CUF seeks to move to a full federal system with three governments: one for the mainland, one for Zanzibar, and one for the United Republic. The proposed draft, devised after lengthy public debate, had endorsed this proposal, but final approval was blocked by the Constitutional Assembly, which has a majority of mainland CCM members. A second factor is the discovery of natural gas off the Tanzanian coast, which has intensified rivalry between the mainland and Zanzibar as to who should control potential revenue, should oil or gas be found within Zanzibar’s territorial waters (exploration in Zanzibar’s blocks has been delayed by political wrangles). A third factor has been the rise of Islamist influence in Zanzibar over the last 20 years, especially among disgruntled youth, who feel that they are treated as second-class citizens, denied government jobs and scholarships, and cheated of genuine political voice. These tensions have not only intensified the political rivalries within Zanzibar, which have been controlled by the CCM (and its Afro-Shirazi Party predecessor) since the January 1964 revolution, but have worsened relations between the archipelago and the Union government. In the most recent electoral run-up, CCM hardliners played to these fears, portraying CUF as a party of the Islamists and warning that a CUF government would ultimately demand the breakup of the Union and weaken CCM’s political hold on mainland Tanganyika.

Elements within the CCM on Zanzibar would like, or at least accept, a three-government solution and a fully federal system and are as eager as CUF for the islands’ government to get its hands on any oil or natural gas windfall, but they are determined not to cede power to CUF.

The CCM’s stronghold is the Hadimu areas of southern and eastern Unguja, populated predominantly by poor farmers and fishermen. There are historic pockets of CUF support in the far north, parts of the west coast, and in the capital, Zanzibar Town, with one-fifth of the archipelago’s total population. Stone Town, its historic core, is an opposition stronghold. CUF’s center of power, however, is on Pemba, the main northern island. Development and in recent years the expansion of the tourist industry are centered primarily on Unguja, while rural Pemba still lacks basic infrastructure. Historically, ethnic and social relations between Arabs, Shirazi, and mainland African migrants were far more equitable on Pemba than in Unguja, which until the 1964 revolution was dominated by Arab-owned plantation agriculture.

Ethnic divisions have governed all nine Zanzibar elections: the four held under British colonial rule and the five since the return to competitive party politics in 1995. After another outbreak of violence following the disputed 2005 elections, protracted negotiations resulted in a constitutional referendum in 2010, which permitted the formation of a coalition government between the two parties. Consequently, a government of national unity was formed after the 2010 elections, in which CUF’s Seif Shariff Hamad became first vice president in a government headed by Ali Mohamed Shein. This reduced political tensions but failed to address the fundamental divisions.

The October 2015 election was a missed opportunity as it might have enabled the CCM gracefully to relinquish its 50-year-long control over Zanzibar by agreeing to participate in the ongoing Government of National Unity, albeit one headed by CUF leader Seif Shariff Hamad. With nearly half the vote and members of the House of Representatives, the CCM would have continued to exert considerable influence and would have been well placed to negotiate guarantees from CUF about the personal and business interests of its leaders. Instead, the Zanzibar CCM decided to hang onto power. The nomination of Edward Lowassa as the presidential contender for Ukawa, a coalition of the four main opposition parties, including CUF (with its strength in Zanzibar) and Chadema (strongest on the mainland), upped the political stakes on the archipelago. It seemed, for the first time, that the CCM risked defeat not only in Zanzibar but in the Union Parliament. However, the Zanzibar CCM was determined not to lose the election, especially the presidential contest, with its wide powers of appointment. They were backed by elements in the mainland party, including some who believed that a CUF victory would threaten the Union.

Thus, it should have been clear to international observers that the 2015 contest on Zanzibar would be fraught with dangers. Given the ZEC’s partisan behavior in 1995, 2000, and 2005, it should have been anticipated that even if the campaign and voting passed off relatively peacefully, the presidential vote collation process would be vulnerable to possible interference from the Zanzibar CCM.

This, indeed, is what happened. Commonwealth, African Union, East African Community, Southern African Development Community, and European Union observers all praised the orderly nature of the campaign, poll, and count. Seif Sharif Hamad’s declaration of CUF victory less than 24 hours after the close of polls was based on returns from CUF observers in the 54 constituencies where the results are counted—and signed by agents of both parties—in each polling station and was therefore almost certainly accurate. Instead, ZEC chairman Jecha Salim Jecha, a CCM loyalist, voided the elections three days after the vote. He declared that a complete rerun would have to held because of intimidation and fraudulent returns. Troops and police immediately surrounded the counting center before forcibly escorting the deputy chairman of the ZEC from the building. Jecha has failed to produce any evidence to support his claim of massive irregularities.

Tensions have been high on Unguja and Pemba ever since. A curfew is in place, police and soldiers patrol in armored cars, local CCM and CUF offices have been burnt down, and bombs have exploded. More than 100 CUF members, including the director of publicity, have been arrested. All campaign rallies for the rerun have been forbidden.

The controversy has renewed the debate over the extent to which the Zanzibar government and the Zanzibar faction of the CCM are autonomous from the Union Government in Dodoma and Dar-es-Salaam. The original 1964 constitution of the United Republic of Tanzania granted almost complete autonomy to the archipelago, which was heavily overrepresented in the Union Parliament, but the revised 1977 constitution increased the authority of the Union, enabling national armed forces to be deployed on the islands and reducing the autonomy of the Central Bank of Zanzibar. Zanzibar politicians, nevertheless, still play an important role in the internal affairs of the ruling CCM. Zanzibar blocked the nomination of Jakaya Kikwete for the presidency in 1995 despite his winning the first round at the CCM convention.

It remains unclear whether the ZEC acted simply on the instructions of President Ali Mohamed Shein and hardliners in the Zanzibar CCM or with the agreement of the Union government. It seems likely that the Union authorities were sufficiently confident of victory that the Zanzibar CCM acted unilaterally in a desperate attempt to hold onto power. But Dar-es-Salaam’s subsequent silence and newly elected President John Magufuli’s refusal to intervene in the crisis do not bode well. CUF will boycott the election rerun, insisting that it won the original election. This may be a mistake, as little is to be gained by permitting the CCM to gain complete control over the political process possibly for the next five years, but CUF leaders do not want to give legitimacy to what is almost certainly a foregone result.

The fallout from the crisis in Zanzibar will have three effects. First, it may strengthen the mainland opposition’s resolve, which suffered a blow with Lowassa’s defeat by the little known Magufuli. Secondly, it will intensify the debate over the new constitution. Although Zanzibar politicians in both CCM and CUF favor a “three-government” solution that would codify Zanzibar’s position in a federal system, CUF supporters may become increasingly intransigent and push for the breakup of the United Republic, the very fate that the CCM is determined to prevent. Thirdly, Zanzibar’s politics will likely remain violent.

President Magufuli’s image as the new, “clean man” of Tanzanian politics will be damaged, not only in the eyes of Tanzania’s electors but more importantly before the international community. He has already demonstrated a thin skin for criticism by diplomats and the media, but the climate would become far worse if widespread violence in Zanzibar led donors to reduce or suspend aid. At present, Tanzania is a major recipient of virtually all the major strands of U.S. assistance under the President’s Emergency Plan for AIDS Relief, Feed the Future, and Power Africa, among others. Almost one-third of its budget is financed by overseas donors. President Magufuli gained an insight into the potential impact of donor disengagement in December when the United States deferred a vote on selecting Tanzania for a new $472 million compact under the Millennium Challenge Corporation, in part because of concerns about events in Zanzibar. Ultimately, Magufuli may have to make a very hard choice between appeasing the hardliners in his party and donor governments.

Western diplomats should be under no illusions that they will have to play “hardball” with Tanzania if they intend to overcome the CCM hardliners and bring real democracy to Zanzibar after two decades of rigged elections. Tanzania has long been a “donor darling” for the West, which has been reluctant to acknowledge the government’s undemocratic conduct, intolerance of civil liberties, and growing penchant for corruption. Recent legislation has restricted the freedom of the media and the rights of citizens to access information. Last March, Parliament rushed through the Cybercrime and Statistics Acts, which include the provision that anyone who publishes statistics without official permission is liable to a jail term of up to one year. Tanzania has fallen far short of Secretary of State John Kerry’s 2015 description of it as a “model in the region for good governance, democratic ideals, and individual freedoms.” Indeed, at the first sign of a serious electoral challenge, the CCM has resorted to fraud and restrictive legislation.

For its part, however, the Tanzanian government does not take kindly to lectures from the West and fends off international critics with accusations of interference in its national sovereignty. In January, the Ministry of Foreign Affairs issued a letter warning foreign diplomats that its permission was required for appointments with political leaders, members of Parliament, local officials, and grassroots organizations. The circular followed a flurry of meetings between diplomats and opposition leaders to discuss Zanzibar.

The recent actions of the Tanzania government suggest that the CCM is determined to clamp down on its critics. Despite the plaudits he has received during his first months in office, there are limits to what President Magufuli is likely to tolerate. He may remove a few of the most egregiously corrupt officials, but the CCM’s close monitoring of its citizens will probably increase. Unfortunately, Magufuli is likely to be swayed by the CCM hardliners who argue that the ruling party cannot afford to lose control of Zanzibar and that defeat on the islands would set a bad precedent for the mainland. Donors meanwhile, will most likely quietly forget about the problems of Zanzibar and acquiesce in five more years of CCM control there, unless violence escalates to a level that cannot be ignored. Only at that point would the calculus change on both sides, but by then it will be perhaps too late to preserve the United Republic.

David Throup is a senior associate with the Africa Program at the Center for Strategic and International Studies in Washington, D.C.

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David W. Throup