There is a grisly background to the Nov. 12 car bombings of Iran’s embassy in Beirut, Lebanon. That blasts killed 23 people, including an Iranian diplomat, and were aptly denounced as “despicable” by Secretary of State John Kerry.

Iran introduced that indiscriminate weapon, the car bomb, into Lebanon 30 years ago. Apparently in Beirut, what goes around eventually comes around.

Iran’s new defense minister, Brig. Gen. Hossein Dehghan, was the man in charge of the Iranian-backed car and truck bombings in Beirut of the U.S. Embassy in April 1983 and U.S. Marine and French army barracks in October, 1983, killing 375, including 271 Americans.

Gen. Dehghan played a major role in building Iran’s stronghold in Lebanon, the Hezbollah militia.

In 2005, Syria, Iran’s key ally in the area, helped solidify that dominance when it arranged for Hezbollah to set off the massive car bomb in Beirut that killed the anti-Syrian Lebanese Prime Minister, Rafik Harriri.

As former Sen. Joseph Lieberman wrote in a Washington Post guest op-ed Thursday, Iran has long pursued the goal of dominating the Middle East through such terrorist tactics.

So the assault on the Iranian embassy in Beirut could be considered a grim form of poetic justice.

But it was also a dangerous sign that Syria’s civil war is spreading beyond Syria’s borders. While Iran blamed Israel for the bombing, it was in fact carried out by an al-Qaida affiliated group in Lebanon, the Abdullah Azzam Brigades. That band of killers will continue such attacks until Iran pulls its forces out of Syria where they are helping the government defeat the rebels.

The religious dimension to that conflict helps it spread beyond Syria’s borders. Iran, its Hezbollah ally in Lebanon, and Syria’s ruling party follow the Shia tradition. The Syrian opposition, like most Arabs throughout the Middle East, follows the Sunni tradition.

Al-Qaida is a radical Sunni group. It has been active in Syria and resurgent in Iraq, where it is responsible for many attacks on Iraqi Shias. It is strong in Yemen, is active in North Africa and has infiltrated forces into the Sinai where they regularly ambush the Egyptian Army. Now it is showing its teeth in Lebanon.

President Barack Obama’s reluctance to support moderate Sunni rebels in the Syrian civil war opened the door for al-Qaida to re-emerge from its defeats in Afghanistan and Pakistan to claim a role as the Sunni champion in the heart of the Middle East.

Many war-weary Americans were understandably relieved that the president backed away from his stated intention to intervene in Syria.

But ignoring that bloody civil war won’t make it go away.

And as it spreads beyond Syria’s borders, it becomes a growing threat to the stability of the Mideast — and to the international community, including the U.S.