Here's a worrying sign that it's only a matter of time before the next Middle Eastern crisis breaks out

A host of Middle East nightmare scenarios have unfolded in recent years, from chemical warfare toattempted genocide to state collapse to the takeover of significant territory by an unprecedentedly brutal jihadist group.

One of the region's most dangerous frontlines has remained quiet through it all. Even with repeated Israeli strikeson their weapons supply routes and stockpiles inside of Syria, open warfare hasn't broken out between the Lebanese terrorist group Hezbollah and Israel.

Even amid a regional meltdown, the number of rockets that the Lebanese terrorist group Hezbollah has fired on Israel since the conclusion of their summer 2006 war can be counted on one hand.

Few believe that the Israel-Hezbollah front will stay quiet forever. On November 12, Avi Isaacharoff reported for The Times of Israel that Israeli intelligence officials believe Hezbollah now has an arsenal of 150,000 rockets, a 50% increase over an estimate from May 2015 — and that's before sanctions have even been lifted on Iran, Hezbollah's state sponsor.

Hezbollah may be deeply entrenched in the Syrian quagmire at the moment, where it's fighting to preserve the regime of President Bashar al-Assad against various armed groups. But Hezbollah is still stockpiling weapons for use outside of Syria and against a conventional military with sea and air capabilities, "continuing its efforts to acquire SA-17 and SA-22 ground-to-air missiles as well as P-800 Oniks air-to-sea missiles," Issacharoff reports.

Although Israel has repeatedly attacked Hezbollah targets inside of Syria, the group and Iran, its state sponsor, have actually "upped ... efforts to bring in more Iranian weapons," which include "a number of long range Iranian-made missiles capable of striking Israeli cities from north to south."

The Russian weapons system off of which the SA-22 surface-to-air missile is modeled can hit targets at up to 60,000 feet from a distance of up to 12 miles. The P-800, meanwhile, can carry an over 400-pound warhead at distances of up to 180 miles. These weapons are intended to bridge the qualitative gap between an irregular force like Hezbollah and an advanced modern military.

From Israel's perspective, the problem is only going to get worse.

Thomson ReutersAn Israeli soldier stands guard at a checkpoint near the Lebanese-Israeli border.

The nuclear deal signed between Iran and a US-led group of six world powers lifts many of the most stringent sanctions against Iran, including all UN sanctions authorizations. Iran, for whom Hezbollah is a highly effective proxy force, is estimated to receive anywhere between $29 billion and $150 billion in immediate sanctions relief as a result of the deal.

In the long run, the nuclear deal also results in the removal of all ballistic missile and conventional-weapons-trade-related restrictions on the country after eight years. The deal enriches Iran, and eventually gives it access to a wider range of advanced weaponry.

At the same time, the post-nuclear-deal strategic landscape might also make a war likelier. The primary purpose of Hezbollah's rocket arsenal was to deter against an Israeli attack on Iranian nuclear facilities. The nuclear deal means that an Israeli preventative strike is highly unlikely at the moment, given the likely political fallout.

IIPA via Getty ImagesThis image, supplied by the IIPA (Iran International Photo Agency), shows the reactor building at the Russian-built Bushehr nuclear power plant as the first fuel is loaded, on August 21, 2010, in Bushehr, southern Iran.

But this pause in the threat of an Israeli attack also gives Iran and Hezbollah additional time to build up their deterrent capacity. From an Israeli perspective, not acting against Hezbollah increases the future blowback of a strike on Iran's nuclear facilities.

Hezbollah might have reasons of its own to launch a war against Israel. There have been signs that Hezbollah and its Iranian sponsors have been seeking to open a southern front along the Syrian-Israeli disengagement line in the Golan Heights. In January, an Iranian Revolutionary Guard Corps general was killed in an Israeli airstrike, along with the son of the notorious Hezbollah terrorist Imad Mugniyah. On January 17, Hezbollah launched an attack along the Israeli-Lebanese border fence that killed two Israeli soldiers. 

Hezbollah might not want a full-scale war with Israel, but could see some kind of political benefit within Lebanon and the broader Arab world in turning attention away from Syria, and toward Israel. That isn't much of a source of comfort to Israel: Neither Hezbollah nor Israel intended the 2006 conflict to escalate at quickly or as severely as it did. And the costs of a semi-accidental conflict with Hezbollah — a war that many Israeli analysts believe to be all but inevitable — are only increasing as the Lebanese group grows its arsenal.

ReutersHizbollah fighters drive off from the Marjayoun barracks with a tank that belonged to Israel's local militia in south Lebanon on May 24, 2000. Victorious Hizbollah guerrillas took over full control of south Lebanon on Wednesday as Israel completed a hurried withdrawal to draw down the curtain on 22 years of bloody occupation.

So far the stockpiling of 150,000 rockets, including long-range antiair and antiship weapons, hasn't been enough to trigger a major Israeli preemptive strike on Hezbollah's weapons supplies inside of Lebanon. But the group is still moving closer to an unstated Israeli red line, whatever that may be.

Hezbollah is the most capable nonstate armed force in the Middle East, with an advanced arsenal, a powerful state sponsor, and a core of battle-hardened fighters and commanders. The strategic balance may be shifting in ways that Israeli leaders believe they can no longer accept — with worrisome consequences for what's remained one of the Middle East's quietest yet most dangerous front lines.