Three weeks into the Israel-Lebanon war, it appears that something, with apologies to Yeats, is slouching toward Bethlehem. And it's not pretty. Even if this crisis is resolved with an international force and a buffer zone that pushes Hezbollah from the border, the future looks grim.

Far from giving birth to a new Middle East, we may find that we've created one even messier and nastier than the old.

For one thing, the current crisis is showing us just how effective Iran's reach can be. By supplying Hezbollah with long-range rockets, it has changed the strategic equation and created a stunning situation in which a Shiite militia holds its own against one of the world's most effective military powers.

Iran's inclination to meddle — mostly as a way of reminding the Sunni Arab world, Israel and the U.S. that Tehran has cards to play and can inflict pain — will not go away. And ongoing turmoil in Lebanon, Iraq and Gaza will ensure that when Iran next chooses to meddle, it will have fertile ground in which to do so.

A second conclusion to be drawn from the events of recent weeks has to do with the perils of unilateralism. In the Middle East, if you don't get for what you give, there will be no end to the pressure to give more. Israel's unilateral withdrawal from Lebanon in May 2000 and from Gaza in September 2005 may have benefited Israel politically (both domestically and around the world), but it also emboldened Hezbollah and Hamas.

That both groups continue to claim that they alone forced Israel out of Arab territory without agreements or reciprocity is more than just a talking point; it is a powerful inspiration to a younger generation of Arabs and Muslims looking for ways to counter their perceived humiliation at the hands of Israel and, by implication, the United States. It is no coincidence that Palestinians in the West Bank and Gaza were encouraged by Israel's unilateral withdrawal from Lebanon in May 2000 and used it to stoke the flames of their own intifada four months later.

At the same time, Israel's forceful response to the July 12 Hezbollah attack across its border is a clear indication of its own concern about the erosion of its deterrence and the perception of its weakness.

Unless Israel wins a decisive victory over Hezbollah, it is almost unimaginable that any Israeli government would consider significant unilateral withdrawals from the West Bank in the near future. With a unilateral approach blocked and no chance of negotiations with a Hamas-led Palestinian Authority, Israel is faced with the unpalatable alternative of sitting on the West Bank and controlling 3 million Palestinians for some time to come. This will generate increasing anger and bitterness.

The third lesson of recent weeks has to do with the growing challenge to central authority by nonstate actors in the region. The power of Hamas and Hezbollah to affect events highlights a trend that has been building in the Arab world for some time. Iraq has actually been a source of inspiration in this regard: Every day, small armed groups challenge the Iraqi central authority and the U.S. with impunity. It is no coincidence that the two-front crisis Israel now confronts is generated in areas where there is no strong central authority and where armed groups with social and economic agendas usurp the power of the state and create their own fiefdoms. Indeed, Hamas actually serves as the state and the opposition.

Hezbollah may be militarily weakened by this crisis, but it will reap tremendous political benefits from confronting Israel; it also will be able to use Iranian-supplied funds to minister to the needs of those Lebanese who have been displaced as a consequence of Israel's military operations.

The United States did not create the current crisis, but its neglect of the Arab-Israeli arena gives it little leverage to affect the outcome. It has no relationship with Syria; it is engaged in containing Iran; and, by law, it cannot enter into relations with terrorist groups such as Hezbollah and Hamas.

What leverage it does possess — the trust and confidence of Israel and the capacity to restrain it under certain circumstances — it has been unwilling to use so far. Having passed up numerous opportunities to address the Israeli-Palestinian conflict, it has little to show on the one issue that resonates deeply through the Arab and Muslim world. Never has anti-Americanism been higher and Washington's capacity to affect events been lower.

The Israeli-Lebanese war cannot be blamed on the U.S. The Middle East is a dysfunctional place, where conflicts within and between states continue to drive events. Great powers have limited leverage over smaller ones locked in existential conflicts in a dangerous neighborhood. Iraq is a cautionary tale.

But the U.S. is not an innocent bystander. Governing is about choosing, and the administration has chosen priorities — Iraq, Iran, the war against terror — which have taken it far from the Arab-Israeli arena and the core issue of the Israeli-Palestinian conflict. Now it has been drawn in against its will.

But there should be no surprises here. As former Secretary of State James A. Baker III once said: "I could either manage the issue or let it manage me."

Aaron David Miller is a public policy scholar at the Woodrow Wilson Center in Washington and served as an adviser to six secretaries of State on Arab-Israeli peace negotiations. He wrote this commentary for the Los Angeles Times.