Two incidents this week showcase the complexity of the challenges facing Israel on its northern front.In the first, an air strike killed four members of the Islamic State-affiliated Khalid Ibn al-Walid Brigade after a patrol of the Golani reconnaissance unit in the southern Golan Heights was targeted by the organization. Israeli aircraft then targeted a facility used by the group in the Wadi Sirhan area.In the second incident, according to regional media reports, Israeli aircraft operating from Lebanese airspace fired Popeye missiles at targets in the Sabboura area, 8 km. northwest of Damascus.There were no casualties, according to SANA, the official Syrian news agency.London-based Arabic newspaper Rai al-Youm reported that the Israeli strike was targeting a Hezbollah-bound weapons convoy. The paper also reported that Israeli aircraft carried out a second strike on a facility of Syria’s 4th Armored Division, near Damascus.Israel neither confirmed nor denied the second incident. But on a number of occasions over the last four years of war in Syria, Israel has used its ability to operate in the skies over Syria to prevent weapons transfers to Hezbollah in Lebanon from the Syrian regime. It is possible that this incident was the latest act in this effort.These two events are of tactical importance only. Neither is likely at this stage to lead to broader engagements, but they reflect a reality in which some of the world’s most powerful non-state military organizations are deployed close to Israel’s border with Syria, making war against one another while planning and organizing for a future war against the Jewish state.The Khalid Ibn al-Walid Brigade is a franchise of the Islamic State. It was formed from the merger of two Salafi organizations operating in southern Syria – the Shuhada al-Yarmuk group and the Muthanna organization. The group controls an area of the border east of the Golan Heights, from south of the town of Tasil, down to Syria’s border with Jordan.From this area, the brigade is conducting a war against the Syrian rebels to its north. It does not fight the forces of the Syrian government because they are not deployed in its immediate vicinity.Israel has long eyed the Islamic State-affiliate with particular suspicion, expecting that sooner or later a clash would be inevitable. This week it came.The volume of the Israeli response was clearly intended to reestablish deterrence against the Sunni jihadis, with the hope that it will cause them to think again before engaging with Israeli forces.Islamic State is facing battle for survival in its main domains farther north and in Iraq and it is unlikely that it is in a position to contemplate opening a front against a newer and more powerful enemy farther south.The non-Islamic State rebels who control the rest of the border, with the exception of a small-regime controlled part at the northern edge near Beit Jinn, are of lesser concern to Israel. Indeed, a relationship of tolerance and cooperation exists between Israel and elements among those rebels.Israel’s main concern, rather, is the Iran/Assad/Hezbollah side. The reported strikes in the Damascus area, if they took place, were the latest incidents in a limited Israeli campaign against these elements intended to produce two outcomes: first, to limit the transfer of complex weapons systems to Hezbollah, and second, to keep the Iran-supported militia and its allies from replacing the rebels along the borderline.As of now, it is difficult to assess the extent of the success of the first objective.Hezbollah is known to now possess advanced SA-22 anti-aircraft missiles and Yakhont anti-ship missiles. So, as might be expected, it appears that the sporadic Israeli efforts have not succeeded in sealing the Lebanese-Syrian border from efforts by the Assad regime and Iran to supply their ally to the west.Regarding the border, however, as of now, it remains almost entirely out of government hands, reflecting greater Israeli success.Nevertheless, Israeli planners are carefully observing events farther north. President Bashar Assad’s regime, with Russian help, is set to reconquer the northern city of Aleppo. This will represent the greatest setback for the rebels since 2012. Once the reconquest of eastern Aleppo is completed, regime forces will hope to move against remaining areas of rebel control in Idlib Governorate.If they succeed also there, then eventually the southern front will come back on to the agenda. At this point, the Israeli concern will be that similar methods to those that helped the regime to prevail elsewhere will be used here too. The Russian entry into the Syrian arena has tilted the balance for the regime and complicated the picture from Israel’s point of view. It is Russian air power that is enabling the regime to advance in the north. If employed in the south, it can be expected to eventually produce similar results.It is probable that Israel will be quietly lobbying Moscow to take account of Israel’s security needs on the border when contemplating action in the south. The Russians are not hostile to Israel, but will act according to how they perceive their own interests. Their decision as to whether to allow Assad to reconquer the southwest of his country – and by so doing to allow Iran and Hezbollah to reach the border with Israel – will be decisive.Of course, even in the worst case scenario in which they decide to allow this, the task facing Israel on the border will not fundamentally change. It will mean that instead of needing to deter hostile but relatively weak Sunni jihadi forces from contemplating action against the hated Zionists, Israel will need to deter hostile and less weak Shi’ite jihadis with the same intentions.Iran/Hezbollah and Islamic State agree about relatively little, but on the goal of destroying Israel and returning Jerusalem to Islamic rule they are entirely in consensus.Israel, naturally, prefers the weaker, non-state enemy in close proximity to the stronger. The events of this week show that it is engaged in a tacit, ongoing, unstated and limited war against both.