As U.S. Marines and international troops moved into Port-au-Prince last week, there was great relief that a bloodbath had been averted. Now the international community must help Haiti rebuild a government and get back on the path to democracy. How smoothly that will go depends on many factors: whether the rebels make good on their promise to disarm; whether Aristide's polarizing claims of a White House-ordered "kidnapping" have any consequences; and how quickly aid can be restored, to alleviate the nation's wrenching poverty.

But whatever policy is pursued in Haiti, it cannot ignore the country's conjoined twin on the island of Hispaniola: the Dominican Republic.

Policymakers too often view the Spanish-speaking Dominican Republic only in the light of its turbulent, more densely populated and much poorer neighbor to the west. Yet even as order is restored in Haiti, the Dominican Republic is struggling with a political and economic crisis of its own, the outcome of which will be crucial to both nations. Failure to avert a democratic breakdown there could not only undermine any Haiti policy, but also increase the flow of boat people to the United States.

As Haiti's crisis escalated last month, U.S. officials were preparing 50,000 new beds at our Guantanamo Bay base in Cuba to accommodate a feared wave of Haitians. Yet a steady stream of boat people was already leaving the Dominican Republic, in numbers dramatically higher than in previous years and larger than the number of Haitians. In January and February, the U.S. Coast Guard intercepted 1,977 Dominicans, compared with 717 Haitians. Over the past three years, 300 Dominicans have gone missing while attempting the dangerous 75-mile journey to Puerto Rico across the shark-infested Mona Passage aboard rickety wooden motorboats called yolas.

As the country heads toward presidential elections in May, Dominican democracy, barely a decade old, is in a tenuous state. The administration of President Hipolito Mejia has more than doubled the country's foreign debt in less than four years -- from $3.7 billion to $7.6 billion -- and is already having trouble keeping up with interest payments. The country's second-biggest bank collapsed last year, a $2.2 billion disaster that sideswiped the economy and devalued the peso from 17 to more than 50 to the U.S. dollar. The bank's demise uncovered a vast network of corruption and payoffs; though Mejia's Dominican Revolutionary Party (PRD) was not the only one implicated, Dominicans blame the ruling party.

In a poll last October of Latin American public opinion on their leaders' performance, Mejia had the lowest approval rating in the hemisphere; even Peruvian President Alejandro Toledo, often cited as the lowest at 7 percent, edged out Mejia, who scored only 6 percent. The PRD has fractured over who its candidate should be in May, but concerns have arisen that Mejia may try to steal the election. Recently, a local newspaper revealed that voter rolls authorized one man to vote at three different stations, only one small example of the kind of high jinks Dominicans fear could smear their recently won democracy.

An election crisis could jeopardize not only the country's stability, but also international efforts to help Haiti at a time when Dominican support has been crucial. As Haiti's crisis played out, the Dominican military helped evacuate foreigners. The Dominican Red Cross helped get needed aid to Haiti. Though it closed the border and doubled the number of troops posted there to prevent an influx of refugees, the Dominican government did allow Haitians in on market days twice a week to shop -- very important for humanitarian reasons.

Before Aristide flew into exile last week, he was fond of saying that Haiti and the Dominican Republic were like two wings of the same bird. Similarly, Mejia likes to say the two are in a marriage with no possibility of divorce. These words bespeak a fragile, and now threatened, truce that has held for the past decade. In that period, Dominicans have taken the lead in pursuing joint border development projects and warming the tone between the two countries. Dominicans have worked with the Haitian government to legalize the status of several hundred thousand Haitian migrants living in the Dominican Republic, a long-standing sore point.

After international criticism of the mass deportations of Haitians and dark-skinned Dominicans it had periodically carried out, the Dominican Republic took steps to reduce abuses and signed an agreement with the Inter-American Commission on Human Rights. Dominican investors even opened an industrial park in Ouanaminthe, on the Haitian side of the northern border, to employ Haitian workers.

The new crises in both countries have put this progress at risk, and Haiti's uprising has stirred old animosities. Until former dictator Jean-Claude "Baby Doc" Duvalier gave an interview from France saying he wanted to return to Haiti, rumors swirled in Haitian cyberspace that he was living in the Dominican Republic. When Haitian rebel leaders Guy Philippe and Louis Jodel Chamblain returned to Haiti from Dominican exile last month, Aristide denounced the Dominicans for allowing them to cross back into Haiti. Rumors in late February, strenuously denied, insinuated that Dominican military officials had known of and condoned rebels training within their borders. The Dominicans, for their part, suspect Haitian rebels of killing two Dominican soldiers at the border. Meanwhile, the Dominican Republic is bracing for a potentially destabilizing flow of refugees.

Turmoil on either end of the island has always spilled over to the other. After Haiti expelled France in 1804, Haitian President Jean-Pierre Boyer encouraged Dominican independence from Spain, but then occupied the Dominican Republic for 22 years. In the 1940s, longtime Dominican dictator Gen. Rafael Trujillo, a master of meddling in Haitian politics, sent his spy chief to Port-au-Prince to root out Dominican political opponents. This tradition continued through Dominican support for the Haitian military leaders who deposed Aristide in a 1991 coup.

In 1994, after octogenarian strongman Joaquin Balaguer pulled off a massive election fraud in the Dominican Republic, the international response to that crisis was muted because of the need for Santo Domingo's cooperation on Haiti. Balaguer agreed to help police the Haitian border and was allowed to stay in office for half his term. When he stepped down in 1996, a concerted Dominican effort with international support carried off the country's first-ever clean elections.

Not surprisingly, suspicions between Haitians and Dominicans remain. In 2000, a popular Haitian Carnival song warned that Dominicans wanted to take over Haiti. When Chamblain and Philippe returned to Haiti, a young Haitian reporter asked me whether I thought rumors that the Dominicans were using the crisis as a pretext to take over her country were true. No, I told her, laughing. For a long time, many Dominicans would have preferred exactly the opposite: that Haiti not share the same island. (Indeed, a Dominican reviewer of my book about the two countries complained on that I was wrong to include both in the same volume.)

Accusations that the Haitian exiles trained openly and received arms in the Dominican Republic could undermine recent improvements in the countries' relations, as could Aristide's claims that the United States forced him out. In the unlikely event that Aristide's accusations take hold -- they died down somewhat after the Central African Republic asked Aristide to put a lid on it -- the Dominican Republic could come under scrutiny due to the accusation by Aristide's Miami lawyer, Ira Kurzban, that the United States armed the Haitian rebels with some of the 20,000 M-16s supplied to the Dominicans in 2002 for narco-policing and border patrol efforts -- a charge the State Department denied to me as "absurd."

Though an all-out military conflict has been averted in Haiti, the prospect of an exodus to the Dominican Republic will persist until a modicum of political and economic stability is established. A refugee processing center in Haiti or at the border to identify legitimate political asylum cases would reduce the number of Haitians trying to flee to the Dominican Republic. Restoring aid to Haiti quickly will ease the pressure on its neighbor from economic refugees. In addition, humanitarian aid plans should not neglect the border and other areas of the Dominican Republic with large Haitian populations. And the international community should offer support immediately to ensure clean elections in May, including financing for an independent audit of voter rolls as well as international observers.

The success of our Caribbean policy is often measured in the numbers fleeing its island nations. By that measure, Hispaniola's tally is discouraging: The Dominican Republic and Haiti have each sent more than 1 million migrants to the United States. In recent months, desperate Haitians and Dominicans have often been found, quite literally, in the same boat: not the most encouraging metaphor for their two nations, but an apt description of the mutual challenges that lie ahead.

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Michele Wucker is a senior fellow at the World Policy Institute and the author of "Why the Cocks Fight: Dominicans, Haitians, and the Struggle for Hispaniola" (Hill & Wang).

One island, two nations, a stormy co-existence.