The Hamas victory over Fatah in Gaza on June 14 has great importance for Palestinian Arabs, for the Islamist movement, and for America. It has rather less significance for Israel.

Tensions between Fatah and Hamas are likely to endure and, with them, the split between the West Bank and Gaza. The emergence of two rival entities — “Hamasstan” and “Fatahland” — is the culmination of a long-submerged conflict; noting the two regions’ fissiparous tendencies in 2001, Jonathan Schanzer predicted it “would not be all that surprising” were the Palestinian Authority to divide geographically.

Subsequent events did indeed pull them apart:

• The anarchy that began in early 2004 spewed forth Palestinian Arab clan chieftains and criminal warlords.

• Yasser Arafat’s death in November 2004 removed the transcendentally evil figure who alone could bridge the two regions.

• Israel’s withdrawal from Gaza in mid-2005 deprived Gaza of its one stabilizing element.

• Hamas’s victory in the Palestinian Authority elections of January 2006 provided a strong base from which to challenge Fatah.

Assuming Fatah remains in charge on the West Bank (where it is arresting 1,500 Hamas operatives on a detainee list), the two rival factions have replaced the single Palestinian Authority. Given the expedient nature of Palestinian Arab nationalism and its recent origins (it dates specifically to 1920), this bifurcation potentially has great import. As I have noted, “Palestinianism” being so superficial, it could “come to an end, perhaps as quickly as it got started.” Alternate affiliations include pan-Islam or pan-Arab nationalism, Egypt, Jordan, or their own tribes and clans.

Internationally, Fatah and Hamas engaging in war crimes against each other punctures a supreme myth of modern politics: Palestinian Arab victimization. Further, as these two “Palestines” squabble over control of, say, the United Nations seat granted in 1974 to the Palestine Liberation Organization, they damage a second myth: that of a Palestinian state.

“The Palestinians have come close to putting, by themselves, the last nail in the coffin of the Palestinian cause,” the foreign minister of Saudi Arabia, Saud al-Faisal, observes.

A Palestinian Arab journalist notes sarcastically, “The two-state solution has finally worked.”

In contrast, the Islamist movement gains. Establishing a Hamas bulwark in the Gaza Strip gives it a beachhead at the heart of the Middle East from which to infiltrate Egypt, Israel, and the West Bank. The Hamas triumph also offers a psychological boost for Islamists globally.

By the same token, it represents a signal Western defeat in the “war on terror,” brutally exposing Prime Minister Sharon’s shortsighted, feckless unilateral-withdrawal policy from Gaza, as well as the Bush administration’s heedless rush to elections.

As for Israel, it faces the same existential threat as before. It gains from Hamas’s near-isolation from the West, from the fractured Palestinian Arab movement, and from its having a single address in Gaza. It also benefits from having an enemy, Hamas, that is overt in its intention to eliminate the Jewish state, rather than dissimulating, like Fatah. (Fatah talks to Jerusalem while killing Israelis, Hamas kills Israelis without negotiations; Fatah is not moderate, but crafty; Hamas is purely ideological.) But Israel loses when the fervor, discipline, and stern consistency of totalitarian Islam replace Fatah’s incoherent, Arafatian mishmash.

The Fatah-Hamas differences concern personnel, approaches, and tactics. They share allies and goals. Tehran arms both Hamas and Fatah. The “moderate” terrorists of Fatah and the bad terrorists of Hamas equally inculcate children with a barbaric creed of “martyrdom.” Both agree on eliminating the Jewish state. Neither shows a map with Israel present, or even Tel Aviv.

Fatah’s willingness to play a fraudulent diplomatic game has lured woolly-minded and gullible Westerners, including Israelis, to invest in it. The most recent folly was Washington’s decision to listen to its security coordinator in the region, Lieutenant General Keith Dayton, and send Fatah $59 million in military aid to fight Hamas — a policy that proved even more bone-headed when Hamas promptly seized those shipments for its own use.

One of these days, maybe, the idiot-savant “peace process-ers” will note the trail of disasters their handiwork has achieved. Instead of mulishly working to return Fatah and Jerusalem to the bargaining table, they might try focusing on gaining a change of heart among the roughly 80% of Palestinian Arabs, those still seeking to undo the outcome of the 1948–49 war by defeating Zionism and constructing a 22nd Arab state atop Israel’s carcass.

Ehud Barak, Israel’s brand-new defense minister, reportedly plans to attack Hamas within weeks; but if Jerusalem continues to buoy a corrupt and irredentist Fatah (which Prime Minister Olmert has just called his “partner”), it only increases the possibility that Hamasstan eventually will incorporate the West Bank.

Mr. Pipes is the director of the Middle East Forum.