JERUSALEM, OCTOBER 12

In the three and a half decades since it began as an underground militant group, Hamas has pursued a consistently violent strategy aimed at rolling back Israeli rule - and it has made steady progress despite bringing enormous suffering to both sides of the conflict.

But its stunning incursion into Israel over the weekend marks its deadliest gambit yet, and the already unprecedented response from Israel threatens to bring an end to its 16-year rule over the Gaza Strip.

Israel's retaliation for the Hamas assault, in which over 1,200 people were killed in Israel and dozens dragged into Gaza as hostages, will likely bring a far greater magnitude of death and destruction to Gaza, where 2.3 million Palestinians have nowhere to flee and where 1,100 have already been killed.

Hamas officials say they are prepared for any scenario, including a drawn-out war, and that allies like Iran and Lebanon's Hezbollah will join the battle if Israel goes too far.

'I don't think anyone really knows what the endgame is at the moment,' said Tahani Mustafa, a Palestinian analyst at the Crisis Group, an international think tank. But given the amount of planning involved in the assault, 'it's difficult to imagine they haven't tried to strategize every possible scenario.'

Shaul Shay, an Israeli researcher and retired colonel who served in military intelligence, said Hamas 'miscalculated' Israel's response and now faces a far worse conflict than it had anticipated.

'I hope and I believe that Israel will not stop until Hamas has been defeated in the Gaza Strip, and I don't think that this was their expectation before the operation,' Shay said of Hamas.

FROM UPSTART INSURGENCE TO PROTO-STATE

From its establishment in the late 1980s, on the eve of the first Palestinian intifada, or uprising, Hamas has been committed to armed struggle and the destruction of Israel. At the height of the peace process in the 1990s, it launched scores of suicide bombings and other attacks that killed hundreds of Israeli civilians. The violence only intensified with the breakdown in peace talks and the far deadlier second Palestinian uprising in 2000.

Hamas attacks were met with massive Israeli military incursions into the occupied West Bank and Gaza that exacted a far heavier death toll on Palestinians. But as the violence wound down in 2005, Israel unilaterally withdrew its soldiers and some 8,000 Jewish settlers from Gaza, while maintaining tight control over access to the enclave by land, air and sea.

Hamas claimed the withdrawal as vindication for its approach, and the following year it won a landslide victory in Palestinian elections. In 2007, after bitter infighting, it violently seized Gaza from the internationally recognized Palestinian Authority.

Over the next 16 years, through four wars and countless smaller battles with Israel that rained devastation upon Gaza, Hamas only grew more powerful. Each time it had more rockets that traveled farther. Each time its top leaders survived, securing a cease-fire and the gradual easing of a blockade imposed by Israel and Egypt. In the meantime, it built a government - including a police force, ministries and border terminals with metal detectors and passport control.

And what of the thousands of Palestinians killed, the flattened apartment blocks, the crumbling infrastructure, the suffocating travel restrictions, the countless dreams deferred in Gaza, a 40-kilometer (25-mile) coastal strip sandwiched between Israel and Egypt?

Hamas blamed Israel, as did many Palestinians. The Hamas government has seen only sporadic protests over the years and has quickly and violently suppressed them.

NEGOTIATIONS AND THEIR DISCONTENTS

If Hamas' armed struggle against Israel looks like a failure - or much worse - consider the alternative.

The Palestinian leadership in the West Bank recognized Israel and renounced armed struggle over three decades ago, hoping it would lead to a state in the West Bank, Gaza and east Jerusalem, territories seized by Israel in the 1967 Mideast war.

But the talks repeatedly broke down, partly because of Hamas' violence but also because of Israel's relentless expansion of settlements, now home to more than a half million Israelis. There have been no serious peace talks in well over a decade, and the Palestinian Authority has become little more than an administrative body in the 40% of the occupied West Bank where it is allowed to operate.

Palestinian President Mahmoud Abbas, an 87-year-old moderate, has been powerless to stop settlement expansion, settler violence, home demolitions or the unraveling of longstanding arrangements around a sensitive Jerusalem holy site. He has been sidelined during every Gaza war - including this one - and the Palestinian Authority is widely seen as a corrupt accomplice to the occupation.

'Palestinians have tried everything from elections to boycotts to the (International Criminal Court) to engaging in a supposed peace process,' said Mustafa, of the Crisis Group. 'You've had one of the most conciliatory leaderships in the entire history of the Palestinian national movement, and that still hasn't been enough.'

Still, the scale of last weekend's attack takes Hamas' approach into uncharted territory.

'It is unclear what Hamas' endgame is beyond either fighting to the death or liberating Palestine,' said Hugh Lovatt, a Mideast expert at the European Council on Foreign Relations.

The latest attack marks a 'complete strategic rupture,' he said.

'Despite conducting attacks against civilians in the past and fighting previous wars against Israel, (Hamas) did also simultaneously engage in political tracks,' including negotiations with Abbas' Fatah movement and even tacit coordination with Israel, Lovatt said.

'Now it appears to have fully embraced open-ended violence as its long-term strategic choice.'

FOR ISRAEL, VICTORY COULD AGAIN PROVE ELUSIVE

Israel appears increasingly likely to launch a ground offensive in Gaza. It could reoccupy the territory and try to uproot Hamas, in what would surely be a long and bloody counterinsurgency. But even that might just drive the group - which is also present in Lebanon and the West Bank - back underground.

And Hamas has a horrifying trump card that could give Israel pause.

Hamas and the more radical Islamic Jihad militant group are holding some 150 men, women and children who were captured and dragged into Gaza. Hamas' armed wing claims some have already been killed in Israeli strikes and has threatened to kill captives if Israel attacks Palestinian civilians without warning.

Hamas may succeed - as it has in the past - at trading them for thousands of Palestinian prisoners held by Israel in a lopsided deal that Palestinians would see as a triumph and Israelis as agony.

Israel has faced virtually no calls for restraint in the wake of the Hamas attack, but that could change if the war drags on.

In the end, the two sides could find themselves returning to the status quo: An internationally mediated truce, with Hamas ruling over a devastated and aid-dependent Gaza, and Israel redoubling security along its frontier.

That too, for Hamas at least, would look like a victory.