A big event in the Sunni Arab branch of the Middle East and an equally big event between the House of Saud and Assad.
Their relations began to fray during the Iran-Iraq war as the Assad’s sided with Iran, and aided them, while the Saudis backed Iraq. They continued to fray over internal conflict conditions in Lebanon, as Iran and Assad backed Hezbollah against Sunni interests there.
Assad, from his point of view, is using Iran and Hezbollah as counterbalance against his Sunni majority - which has always been at the heart of civil war attempts against the Assad family, and often with the Syrian Muslim Brotherhood playing a major role.
Iran, from its point of view is using Assad, for their own strategic religious interests and for their military interests against Israel.
In spite of all that, both the Saudis and the Mullahs of Tehran think of Assad as religiously an infidel - not an approved truly Shia Muslim and not and approved Sunni either.
The House of Saud along with the Gulf states and Erdogan were full backers in the destabilization of Syria, which drew Assad even closer to the Mullahs of Tehran.
Assad could hold out some carrots to the Saudis, like less improvement of Assad’s relations with the Mullahs of Tehran, if it wants anything from the Saudis besides the formal exchange of diplomats.
Theirs is always a relationship to watch.
None of the supposed religious differences mean a thing, the political class always does what it does to maintain power, regardless of the political system (or alleged political system, as in the US), thus, Iran supports jihad of all stripes, all the time, in many places, including Syria.
Iran's mullahs have occupied and dominated Lebanon for a long while now, during which time their proxies have forced an end to Syria's occupation of parts of Lebanon and deprived the Assad hereditary dictatorship of a nice source of income.
During the Gulf War, Saddam's pilots flew what remained of the Iraqi airforce into Iran, which had only a pretense of an airforce after ten years of mullahcracy. Most of those planes were never returned. Some of Slick Willie's buddies in Jihadislavia helped Iraq evade sanctions by maintaining what was left (or newly acquired) of its airforce.
The Iranian proxies in Lebanon were sent into battle in Syria, as were press-ganged Afghans who'd sought refuge in Iran (talk about having one's life turn to doodoo, Iran was their best option), because the body bag syndrome in Iran's misadventure in Syria was further undermining the already miserable conditions in Iran and creating political unrest, or rather exacerbating it.
When the Russians arrived in force, Iran didn't take long to pull out and redeploy much of its expeditionary force. Putin has no out plan, and probably doesn't care if he does or not. After enough time, a Russian withdrawal may not look like a tail-between-the-legs flight as the Afghan debacle did. But until then, the Russians are stuck there, trying to outwait the Iranians. The expedient relationship between the Russians and Turks (in Syria and in Libya, and eastern Africa) may be the most remarkable development all.