It was 25 years ago on October 23 that a suicide bomber blew up the Marine compound in Beirut, killing 241 men. My men.

The 21,000 pounds of explosives caused the largest single-day loss of life for the Corps since Iwo Jima in 1945. It marked the start of a series of carefully coordinated attacks - initiated largely by Iran - that have plagued Americans in that region ever since. And the threat continues today.

The recent revelations that Tehran is providing sophisticated weaponry that is killing US Marines and soldiers in Iraq and Afghanistan should come as no surprise. Iran has been waging war against the United States for well over a quarter-century - from the Iranian hostage crisis in 1979 to today. Over the years, it has generously supported terrorist groups from al Qaeda and Hezbollah to Hamas and the Palestianian Islamic Jihad.

Examples of Iran's war-making abound. It has supported Hamas' rocket launches and other attacks into Israeli villages across the Gaza border. It has supplied weapons to Hezbollah in Lebanon - not only to challenge the legitimacy of the duly elected government there, but to prepare for the next Arab war with Israel.

It has supported Syria in incessant efforts to destabilize Lebanon and Iraq. It has supported the Taliban in Afghanistan against NATO forces. And it has used the Iranian Revolutionary Guard Corps' Quds Force to help train, equip and finance Iraqi Shiite and Sunni extremist militias warring on Coalition forces.

Just recently, Hezbollah instructors trained Shiite militiamen in remote camps inside southern Iraq and planned some of the most brazen attacks against US-led forces.

Iran has evolved as a major player in the Middle East, with growing influence. Its proxy war with Israel - only one front in a larger conflict - has increased Iranian popularity throughout the Arab world. (Nor does Tehran's ability to cause trouble with impunity augur well for the peace process.)

With its links to the Taliban and its weapons-smuggling in Iraq and Afghanistan, Iran has been able to wreak havoc via its insurgent proxies while avoiding any blame or retribution itself. Such diversions also draw attention from Iran's primary objective of developing a nuclear weapon.

Here's how to connect the dots on Tehran's involvement in such efforts:

In August 2005, Mustafa Mohammad-Najjar (who'd been commander of the Islamic Revolutionary Guard expeditionary force that supported the Beirut attack in 1983) was named the new defense minister of Iran. In that job, he is most certainly involved in global terrorist attacks and the acquisition of nuclear weaponry.

Iran will likely use its favorite proxy, Hezbollah, to carry out future attacks against the West, including the United States. Najjar's long association with the late terrorist mastermind Imad Fayez Mugniyah lends credence to this probability. We could well find ourselves the target of a weapon of mass destruction right here in the United States that was planned and executed by some of the same players who carried out the '83 Beirut attacks.

Soon after Najjar became defense minister, Brig. Gen. Ahmad Kazemi was appointed to lead the Guard's ground forces. He is Najjar's close confidant and fellow alumnus of the Iranian Revolutionary Guard's Lebanon contingent.

Today, Lebanon has again become a battlefield for insurgents to settle their disagreements. The state-within-a-state that the Palestine Liberation Organization created in the late 1970s has been replaced. The Iranian model, establishing Hezbollah as a proxy, has proven more successful.

Hezbollah's development and growth suggest that Iran and Syria settled in 1983 on a long-range strategy to increase their influence in the region and the world. The operational and training base established by the Iranian Revolutionary Guard that year remains a hub of activity.

As the nation remembers the 1983 attacks on the Marine compound, Americans should also keep in mind how the tragedy came about, and who was - and still is - responsible for preventing the peace that has never come.

Iran isn't just another harmless bully in the Middle East. It's an impediment to peace - and a threat to the United States.

This article is adapted from the October issue of Proceedings, the flagship magazine of the US Naval Institute.