Columnist

Saudi Arabia appears to be committing the original sin of modern Middle East politics — fighting its regional wars in Lebanon and driving that fragile country once again toward civil strife.

Saudi Crown Prince Mohammed bin Salman's target in Lebanon is Hezbollah, the nation's dominant political force, which is backed by the Saudis' nemesis, Iran. Unwilling to risk a direct shot at Tehran, the crown prince is instead attacking Iran's clients in Beirut.

The proxy battle has escalated over the past week. First, the Saudis pressured Lebanese Prime Minister Saad Hariri to resign last Saturday; hours later, MBS, as the 32-year-old crown prince is known, launched sweeping arrests of rival princes and business leaders in Riyadh, creating an uproar across the region. On Thursday, the Saudi government told its citizens to leave Lebanon and advised against future travel there.

For a Sunni Arab world that fears and loathes Iran, the moves by MBS will probably be popular. He's emerging as the strongest (if also the most impulsive) Sunni leader in decades, exercising a kind of raw power at home and in the region that hasn't been seen since Iraq's Saddam Hussein.

The Saudi moves have rattled the Lebanese political class but haven't panicked the financial sector. Riad Salameh, the governor of Lebanon's central bank for the past 25 years, said recently that the monetary authorities had more than $44 billion in reserves, enough to ensure stability. That calmed the markets.

Lebanese officials fear that what's next is a broader economic quarantine on Lebanon, much as Saudi Arabia has imposed on Qatar. Lebanese sources told me Thursday in telephone interviews that the Saudis want to force Hezbollah to leave the cabinet and parliament. That's understandable for Riyadh, but not realistic.

Saudi Arabia's real leverage is that about 500,000 Lebanese work in the Gulf, sending home roughly $3 billion annually, a tide of remittances that keeps Lebanon's financial and property markets afloat. If those Lebanese were expelled, a dramatic downward spiral would begin.

For Lebanon, this is a familiar story. Since the 1950s, regional and global powers have manipulated the country's all-too-pliable sects for their own advantage.

The Sunnis were played by Egypt's Gamal Abdel Nasser and then, catastrophically, by the Palestinian leader Yasser Arafat, whose challenge to the central government triggered the 1975-1976 civil war. The Israelis battled the Palestinians in Lebanon using Christian and Shiite Muslim proxies and finally invaded outright in 1982. The Syrian regime held Lebanon hostage from 1976 until 2005, when enraged Lebanese demanded they withdraw after the assassination of Rafik al-Hariri, Saad's father.

Hezbollah emerged as the dominant force in Lebanon partly because of the instability that followed Israel's unwise 1982 invasion. The Iranian-backed militia has subverted Lebanese democracy and been a dangerous forward outpost for Iran's power. When the Syrian civil war began in 2011, many analysts predicted that a frail Lebanon would tumble back into chaos. But it hasn't happened — yet — because Hezbollah worked quietly with Saad Hariri and other Lebanese leaders to keep a lid on unrest.

Can such quiet cooperation continue? Not if the Saudis sabotage the country's economy in what they describe as an effort to punish Hezbollah.

For the United States, Lebanon poses what's becoming a recurring challenge — how to encourage MBS's push to modernize the kingdom without letting him drive Saudi Arabia and the region off a cliff.

Call it the MBS conundrum: The headstrong crown prince jumped into what U.S. officials thought was an unwise war in Yemen; it's still raging, despite U.S. attempts to find a settlement. MBS escalated a feud with meddlesome neighbor Qatar; Secretary of State Rex Tillerson has tried unsuccessfully to mediate. This week in Lebanon, the United States was again attempting damage control, as Ambassador Elizabeth Richard pledged $42 million for the Lebanese army and expressed support for "a stable, secure, democratic, and prosperous Lebanon."

The rivalry between Iran and Saudi Arabia has been ripping the fabric of the Middle East since the Iranian revolution of 1979, spawning terrorist movements and proxy wars among Shiite and Sunni allies of the two nations. This sectarian bloodletting seemed unstoppable when a strong, arrogant Iran faced a weak, confused Saudi Arabia.

MBS may hope to become the powerful Sunni leader who could eventually balance the region — and open the way for a grand bargain that would bring stability. That's a desirable outcome. But in the short term, the challenge for Washington is to prevent this would-be strongman from blowing up himself and his neighbors.

Another failed state in the Middle East is not in America's interests.

Read more from David Ignatius's archive, follow him on Twitter or subscribe to his updates on Facebook.