Yesterday, Palestinian President Mahmoud Abbas announced that the Palestinian Liberation Organization's (PLO) leading faction, Fatah, has agreed to a unity pact with its main political rival, Hamas, ending a seven-year rift between the parties.

The news elicited immediate negative reactions from both Israel and the U.S., who consider Hamas a terrorist group and view the agreement as yet another blow against faltering peace talks between Israeli and Palestinian leaders. (Israel essentially ended all peace negotiations upon hearing the news.)

Hamas and Fatah have long held fundamentally opposing viewpoints on several issues, most notably, that status of Israel, which Fatah has tried to work with, but Hamas has officially vowed to destroy. This, however, isn't the first time that Fatah and Hamas have tried to reconcile, in order to strengthen their own Palestinian government. Below is a brief history of their conflict, and the reasons they've remained divided. 

But first, the pact: 

The agreement between Fatah and Hamas came after a day of marathon talks that ended at 3 a.m. on Wednesday. According to Reuters, the new unity government should be in place within five weeks, and national elections are to be held six months after that. Currently, the PLO is led largely by members of Fatah, and has no Hamas representatives — but the new unity government won't have representatives from either side. The Jerusalem Post explains

The new government that will be formed will not include members of either Fatah or Hamas, but rather experts who will prepare the ground for presidential and parliamentary elections on January 15, 2015. Deputy Hamas political bureau chief Musa Abu Marzouk said that there remained "many roadblocks on the way to unity, but the desire for reconciliation is great enough to overcome them."

If the pact holds, it could bring together the Palestinian people and leadership, helping smooth over internal politics and form a unified front against Israel.

The rift: 

Hamas and Fatah have fundamentally different approaches to the state of Israel. Hamas believes the state does not have the right to exist, and Fatah believes it does, choosing to attempt political solutions instead. Fatah has an official stance of nonviolent resistance, while Hamas has consistently uses terrorist tactics against Israel. These (major) disparities have kept the two from joining forces since 2006, when Hamas swept Palestinian elections and unseated Fatah as the ruling party in the Palestinian Authority for a decade. Abbas had just taken his seat as president in an election that followed the death of long-time leader Yasser Arafat, and was slated to finish out the term.

Hamas was not willing to join the PLO, but the group's victory was already a cause for concern in Israel and Washington. The Washington Post reported at the time: 

The arrival of Hamas, formally known as the Islamic Resistance Movement, in the Palestinian Authority as a nearly equal partner will severely complicate Abbas's efforts to begin negotiations with Israel under the U.S.-backed peace plan known as the "road map."

In 2007, the first attempted unity government was dismantled. Hamas seized control of the Gaza Strip following days of violence, and Abbas declared a state of emergency as the government fell apart. Per the Associated Press

Abbas, of Fatah, fired the Hamas prime minister and said he would install a new government, replacing the Hamas-Fatah coalition formed just three months ago. Abbas' decrees won't reverse the Hamas takeover of Gaza. Instead, his moves will enable Fatah to consolidate its control over the West Bank, likely paving the way for two separate Palestinian governments.

Since then, relations between the factions have been in shambles. 

In 2011, both sides agreed to an Egypt-brokered peace deal. But the rival sides couldn't agree on who to name the interim prime minister of the unity government, and the plan fizzled out. Then, in 2012, both sides again signed a reconciliation deal, but failed to follow through on plans to cease hostilities. Later that year, Abbas submitted a bid to upgrade Palestine from an observer to a member state at the United Nations. Hamas sent mixed messages of support for the bid, and Abbas told the international community that if they do not heed his request, Hamas would gain strength — not the best way to make friends with a rival faction. After that, attempts at warming ties were abandoned, until now. 

International reaction 

Israeli and American leaders responded to the latest effort just as they have every other one: with extreme disapproval. Israel has long refused to negotiate with Hamas, and Prime Minister Benjamin Netanyahu said today that Fatah must call off the deal in order to move forward with an Israeli peace plan: "[Abbas] can have peace with Israel or a pact with Hamas — he can't have both." Yesterday, Netanyahu sent out a series of tweets indicating just how seriously he takes the idea of a Hamas-Fatah alliance: 

Secretary of State John Kerry's spokeswoman Jen Psaki called the unity deal "disappointing," adding "The Palestinian reconciliation deal raises concerns and could complicate the efforts to extend peace talks."

Will it last?

Leaders on both sides are hopeful that the pact will be successful. Hamas Prime Minister Ismail Haniyeh called the pact "good news," saying that "the era of division is over." Fatah senior official Azzam al-Ahmed added that "we will forget what happened in the past... the result of the efforts that we have made is clear today as we agreed on all the points that we discussed." 

But some experts are skeptical that this unity deal will have any more success than previous ones, and not just because of the bad precedent. Gaza analyst Talal Okal told Reuters that the future of the deal depends on whether or not the U.S. will extend the deadline for Israel-Palestine peace talks, currently set for April 29. Others see it as an especially risky move at this time, per the New York Times

Tamara Cofman Wittes, director of the Saban Center for Middle East Policyat the Brookings Institution in Washington, said the implications depended on the precise terms of the reconciliation, which have yet to be revealed. “If, and it is a big ‘if,’ Hamas comes under the P.L.O. umbrella in such a way that it accedes to the P.L.O.’s recognition of Israel and the P.L.O.’s signed agreements with Israel,” she said, “that would be historic.” “What would make it horrible is if Hamas were to join the P.L.O. without those kinds of commitments."

Palestinians, meanwhile, are ready for a united government. Hafez Kamel, a resident of the Gaza Strip, told Al Jazeera that "What is important is that the two sides have true intentions to implement [the deal] and do not come under pressure not to. Seven or eight years of suffering by the people are enough."