Do not look at military budget as power status or else Iran would look like a pushover at merely $20B defense budget annually.
This is correct but it applies to countries with a significant domestic defense industry as well as a weak currency relative to the US dollar and/or significantly lower production costs compared to western standards. Of America's allies listed above, only India might fit the bill here. The others do not get much more than America itself out of each dollar invested in their armed forces. Actually, China would also have to be considered more powerful than its nominal defense budget expressed in USD might suggest, given lower production costs compared to its western rivals.
Look at manpower, navy ships, air power.
Manpower alone between India, SK, Japan could muster = 1-1.5M soldiers.
NATO = 750K-1M soldiers (Turkey alone could supply 400K)
US 1-1.5M soldiers
So an allied force could muster 4M soldiers including reservists. Where as China would be at about 1M or so before having to draft regular civilians.
Minbing, the Chinese militia under direct command of the CCP is a parallel military corps of some 8 million, twice the manpower of the described allied force. It's comparable to the Basij.
Despite its rapid transformation, today's People's Republic of China is still consecutive to a founding period marked by Mao Zedong and a heritage of popular mobilization and guerilla warfare (civil war and anti-Japanese resistance before and during WW2). I wouldn't be surprised if these were still taught at Chinese military academies, at least in history classes.
Again this is a “world war” scenario aka a “all hands on decks”
Much would depend on who starts the conflict, whether nuclear weapons are used or not, where exactly it is fought. If China is attacked on its own soil, it will benefit from home turf advantage and all the bonuses defending forces usually enjoy in a military confrontation. Seeing how the attacking side is supposed to muster several times the amount of assets as the defending one, even with the current differential between China and the US plus allies, I would say that boat has almost sailed already.
But this kind of projection is rendered moot by the nuclear factor. A protracted world war scenario would imply that nuclear weapons have lost their deterrent value, that MAD no longer applies. I can't see why this should happen. In the unprecedented event that the US ignores China's nuclear deterrent and attacks the latter even though this ought to mean that several major US cities would get demolished by retaliatory nuclear strikes, then all bets are open that Russia would no longer stay passive because it'd probably interpret such a precedent as a signal that it could well be next, assurances by the west notwithstanding...
In which case Moscow would be likely to go on the offensive, obliterating European NATO members - just the bulk of their armed forces if they're lucky, and major population centers if they aren't. From what I could gather, Russian doctrine with regards to hypothetical war against NATO on European soil seems to be quite nasty: read, multiple strategic and tactical nuclear first strikes, as it relies more heavily on nuclear weapons than during the Soviet era, reason being of course the widened gap in conventional terms between NATO and post-Soviet Russia.
A similar scenario would doubtlessly apply to North Korea, with which China does have a mutual defence agreement. A convenient sort of ally, one which could fulfill a "madman" role - something which isn't lost on the US nor on Japan, which along with California might find itself at the receiving end of a nuclear firestorm unleashed by Pyongyang under the envisaged circumstances.
Between the Allied forces alone, allies could muster at least 5000+ military aircraft to China’s 1500.
Certainly, but here also the question arises what proportion of these 5000 military aircraft belong to US allies vs America's own arsenal. My point is that these allies all put together do not weigh half as much as the US. So to me it's doubtful whether the critical factor is America's network of allies and I'd tend to believe it's more US military power per se.
Apart from that China has not attained parity with the US as of yet. It is however catching up little by little with every passing year. In the meantime, in order to prevent any sort of aggression by the west - which would hardly come in the shape of a direct military attack due to China's nuclear deterrent, Beijing would be wise not to build its doctrine around a USSR-style attempt to surpass the US where the latter's strengths lie, but to mix regular and irregular, symmetric and asymmetric, conventional and nuclear tactics which is precisely what I understand the PLA is doing (by including options such as anti-ship ballistic missiles, extensive drone warfare etc).
Another issue is China like Imperial Japan has an oil problem. (Indeed one reason for Pearl Harbor was oil sanctions had crippled Japanese war machine). While China does have an emergency reserve (exact amount is state secret) securing additional oil to not crash its local economy during a prolonged war effort would be very difficult. Not to mention allies would attack onshore oil storage in the beginning of conflict knowing energy is its weakest link.
Iran and Central Asia. If they attack Iran, then China will automatically have another ally.
Thus we arrive at my original point. Removing nuclear weapons out of the equation (even tactical would open a Pandora’s box that China may be hesitant to do in the beginning). China will need allies, alone it cannot hope to stand against the United effort of the world.
Like I said individually US allies pose not a major threat to China, however together with addition of US the swarm alliance becomes much more lethal in unison and synergistic effect.
If China hesitates to use nuclear weapons in case of a full out US military aggression, then it should never have acquired any. Isn't the whole point of these weapons to deter aggression? if not employed to this effect they make little sense.
By definition nuclear armed states aren't supposed to be defeated by direct war waged on them but through indirect means. Which is how the USSR lost the Cold War. The American empire too, isn't going to fall as a result of someone attacking US soil, but by a combination of internal contradictions reaching unmanageable levels, economic hurdles, imperial overstretching and hubris, strategic miscalculations etc.
Thus until China develops alliances it will never reach world order leader status. Merely economic superpower status which does not exactly translate to world order leader status. It will have big say at the table, but not the FINAL say and that right there is key.
My opinion is that US allies are not what would cause the balance to tip and consequently, that the menace for China emanating from NATO owes primarily to the US itself.
Probably no single party will have a final say as in the power to overrule general consensus between all other sides at the table, should such consensus materialize. But the US's voice would still weigh more. Until China catches up with them, which is matter of time unless some major events achieve to set back China relative to the west. Barring such an eventuality, Beijing will then be able to rely on a relative majorities among powers in order to have its way.