This week’s shock attack by Palestinian militant group Hamas against Israel left the Middle East on a knife’s edge. The world remains focused on Israel’s unfolding military response in Gaza, which in the days ahead will surely prove long, punishing, and unpredictable. But meanwhile, fears of a broader regional war are growing, especially after Iranian Foreign Minister Hossein Amirabdollahian, speaking from Lebanon, explicitly threatened expanding hostilities to new fronts. Such a development risks drawing in the US.

If Lebanese group Hezbollah enters the war against Israel, the hostilities in Gaza will become a sideshow. Hezbollah is the world’s most formidable non-state military. Hamas is but a much weaker underling. In 2006, Hezbollah fought Israel to a standstill following a devastating month-long war. It has since grown into a much more capable and experienced fighting force, boasting up to a hundred thousand fighters and estimated to have a similar number of missiles that can overwhelm Israeli defenses, rain down on its cities, and paralyse its economy.

In such a conflict, Hezbollah may also be joined by other Iranian-backed militias. From Beirut to Baghdad, these groups have been threatening to join the battle in what they refer to as the “merger of all fronts” against Israel. These militias have a combined operations centre in Lebanon and have previously fought alongside each other in next-door Syria. They can be deployed to aid Hezbollah and to attack Israel from Syrian territory.

Whether aided or alone, Hezbollah’s entry into the war will be a game changer for Israel and the region. But this is by no means a forgone conclusion. The memory of the destruction visited upon Lebanon in the last major war with Israel is not lost on the group’s leadership. Thousands of its supporters are already fleeing its heartland in south Lebanon, seeking shelter further north in Beirut.

Iran, despite the heated rhetoric, also has to weigh the risks and benefits of such a devastating confrontation. In its network of militant groups, Hezbollah is the crown jewel and its leading line of defence should Israel strike Tehran’s nuclear programme. Will Iran’s leaders wager Hezbollah’s future to try and rescue Hamas, or will they judge it to be too costly and ultimately too futile of an effort?

To date, the decision for Hezbollah to enter into full confrontation with Israel has not been taken. Instead, Hezbollah is limiting its attacks to levels understood by Israel to be within the tacit rules of engagements. Shelling by both parties remains largely confined to the border zone, sparing major population centers. This week’s killing of three Hezbollah fighters in retaliatory Israeli strikes was followed by Hezbollah targeting a similar number of Israeli soldiers. This remains calculated messaging by fire, with the goals of emphasising deterrence and harassing Israel short of igniting a major war.

In the days ahead, as Israel launches a ground invasion of Gaza, Hezbollah will dial up the pressure and it will be difficult for it to completely avoid an active second front from Lebanon. Still, Israeli leaders can potentially preclude a direct bone-crushing confrontation with Hezbollah if their retaliation remains limited and proportional. Hezbollah can perhaps, in turn, curtail its direct involvement, relegating offensive operations to much less capable Palestinian militants operating from its areas of control.

Imperfect as it may be, such a scenario would preclude much worse outcomes while offering advantages to all sides. Iran and Hezbollah can brandish their resistance credentials and posture to their audiences without plunging Lebanon into a devastating war. And Israel can focus on its strategic objective of destroying Hamas’s military infrastructure without getting sucked into a much broader and more perilous battle.