WWII ends with Allied-Soviet fight

Instability in the Middle East is gonna be part of the reason. The other part is emergent awareness of the serious environmental damage widespread global industrialization is inevitably going to cause if the economic model isn't changed. By the turn of the millennium, North America, Australasia, Europe, Russia, and Northeast Asia are all going to be at developed world living standards, and South America, India, and Southeast Asia at newly-industrialized living standards. After China democratizes and joins the Western club, it is gonna achieve newly-industrialized living standards as well, and the underdeveloped world as we know it is going to be limited to Africa and perhaps the Arab world as well (depending on how the fight against Islamism turns out, the negative economic effects on the region of the switch away from fossil fuels, and possible efforts to compensate). No way they are gonna sustain that kind of global consumerist affluence without wrecking the environment if they don't make the system much more efficient.

Fortunately, ITTL decisive environmentalist policies are going to be much easier to implement than OTL, both because the Western political system is going to be stay bound to post-WWII centrist consensus with no rise of neoliberism, and because the world is going to be much more united politically than OTL. They are first going to pursue a mix of nuclear power, renewable energy sources, energy efficiency, and widespread recycling, but I assume TTL is going to be technologically advanced enough (thanks to its greater development levels) that by the 21st century they may achieve commercially-available fusion power.

Israel exists ITTL and as a matter of fact, it is in a much better situation than OTL. It played a significant role in WWIII as the West's main ally in the Middle East theater (besides Turkey and Persia, but they were overrun by the Russians and their Arab allies, Israel fought them back). Thanks to TTL events in WWII (early fall of the Nazi regime caused many more European Jews to survive), their war of independence (the extra millions of Jew immigrant population helped the Zionists reap a total victory and conquer all of Mandatory Palestine), and WWIII (they helped the West defeat the Russians and their Arab allies in the Middle East, and were rewarded with the Sinai Peninsula, the Golan Heights, northwestern Jordan, the east bank of the Jordan Valley, and southern Lebanon), they have a much bigger Jew population than OTL, more or less all the Greater Israel territory and its resources, and no hostile Arab minority problem since the vast majority of them fled or was expelled. They have a cozy strategic position thanks to their close bond with global NATO as their main regional ally and their western side being protected by the Suez Canal zone under international (i.e. global NATO) administration. Due to their close bond with Europe, they have an excellent chance of joining the EU in the near future.

It bears noting that due to the different course of WWII and the peace settlement that was implemented at its end, the West has developed no political taboo against forced population transfer. Much as in the first interwar period, they deem it an acceptable peace-enforcing measure if done in humane conditions, especially so if done by themselves or other powers they trust. As a matter of fact, they have implemented it several times after WWII and WWIII. And ITTL they are the agents effectively establishing global policy and writing international law. Hence, as far as the non-Arab world is concerned, there is no Palestine problem, the Arab-Israel political and demographic status quo is a done deal, and the Arab irredentist claims enjoy little international support or sympathy. The West fought a world war to suppress this kind of aggressive ethno-nationalist shit, Israel was on the good guys' side and was rewarded, the Arabs fought for the bad guys and paid a price, case closed.

Moreover, the North African wars of independence merged with WWIII and so ended with a Western victory and Europe keeping a few important parts of the Maghreb (more or less the same way Israel did, i.e. European settlers in, Arabs out, except for a few trusted loyalists), even if the victors saw fit to give self-rule to the rest of North Africa. Unfortunately the Arab states aren't in a much better shape than OTL (although they are much less fragmented politically: the Middle East is made up of the EU North African territories, the North African Confederation, Egypt-Sudan, Israel (soon to join the EU as well), the United Arab Kingdom, Turkey, and Persia) since the West neglected to apply them the same extensive postwar reforms they applied to defeated Russia. The sense of frustration, humiliation, and isolation the Arabs experience is only magnified in comparison to OTL, and this may be an important reason for the rise and regional success of Islamism once WWIII defeated and discredited secular nationalism.

Syria (except for the Golan Heights that went to Israel and the northern Kurd territories that went to Turkey), Iraq (except for the Kurd areas that went to Turkey), Lebanon (except for the southern area that went to Israel), part of Jordan (the northwestern portion and the east bank of the Jordan Valley went to Israel), Kuwait, Saudi Arabia, Bahrain, Qatar, UAE, Oman, and Yemen. It was established (with the Hashemites on the throne) as part of post-WWII settlement, suffered a Baathist revolution in the second interwar like Egypt, fought on the side of Russia and China like the rest of the Arabs and lost, and was forcibly restored as a pro-Western monarchy after WWIII. I am not sure if they absorbed Yemen and Oman after WWII or WWIII, but it matters little.

Yep. ITTL WWII Axis-Soviet invasion of the Middle East kind of wiped out the previous status quo in the region, and at the peace table the victors decided to go for a political reset of the region and try something different, more friendly to Pan-Arabism, and hence hopefully more stable: a futile hope, as later events proved, but they did try. They decided to revive the WWI notion of the Kingdom of Greater Syria (Levant and Mesopotamia) with the Hashemite dynasty on the throne. Since the Anglo-Americans were going for a political consolidation of the region, they expected Palestine would go to the Jews, and the Hashemites had important historical ties to Arabia as well, they merged Arabia, Kuwait, and the Persian Gulf states in the new kingdom as well. The Allies came to prefer and trust the Hashemites more than the Saudis to rule the new state, and the reset made the Saudi claims on Arabia irrelevant. The Hashemites just made a better lobbying job with the Anglo-Americans at the right moment than the Saudis. As a matter of fact, given how things turned out and are going to, choice of dynasty was in all likelihood largely irrelevant, and a different House on the throne would not have made a real difference to change events.

My pleasure. As I see it, the Hashemites and the Alaouites have been decent Arab leaders for the standards of the lot, and they had some important historical prestige as dynasties, while the Saudis have been terrible for their people and the world, and they were lucky parvenu that won a few tribal battles too many in the 1900s-1920s. Therefore, since ITTL WWII acted as a kind of reset for the Middle East, I saw fit to implement political butterflies that exalted the former and cast down the latter. It does not matter that much in the bigger picture, since ITTL the Arab world experiences overwhelming trends that overpower even the abilities of the best leaders to check, so even the Hashemites or the Alaouites at their best can do little to stop Baathism or Islamism, or the mayhem that follows. Although at the end of the TL, when global-NATO shall quite possibly be more or less done with stomping out the Islamists, I do not know yet if they shall bother restoring these dynasties yet again into power as parliamentary monarchies and an element of stability, or they shall just go for the federal democratic republic option. As it concerns the Saudis, perhaps they might make a temporary comeback once the Islamists take over in the UAK, if not necessarily or even likely as a ruling royal family, then quite possibly as part of the Islamist ruling elite, given their long-standing ties with the Wahhabi.

Given the circumstances (the Arab world experiencing the twin humiliation shock of European colonialism and the West curbstomping them in WWII), I expect ITTL the Arab lands (and the Af-Pak area) shall be the main source of Islamist trouble in the last quarter of the century. On the other hand, Turkey and Persia have got a fairly different historical experience (no real European colonialism, been conquered by the Russians twice in the World Wars and only experienced the West as liberators twice), so quite possibly both might be resistant enough to the Islamist contagion to be affected by it only peripherally. And it is quite possible TTL Khomeini and his ilk got a Russian bullet during WWII or WWIII well before they could rise to prominence. Then again, resistance to Russian occupation might have been an opportunity for Islamists to expand their power base, same as OTL Afghanistan, so things might go various ways.

They shall probably do, but given the circumstances, default historical judgement on them might vary between "the storm was coming anyway, but their mistakes made it worse" and "they honestly tried, but the task was superior to their abilities". Then again, it might be better if they do get a second (well, third) chance in the end.