I wasn't done my friends... I think 22m technologically advanced soldiers would have won either way :/ I was just showing what was going to happen in a summary.
Numbers and tech have nothing to do with it. They still have to cross geographical distance and deal with resistance at the defensible positions of the country. Whether that be urban warfare where no matter how you cut it takes forever, or in the mountains. And you didn't just conquer two "tiny" nations. You conquered Turkmenistan, Uzbekistan, Kyrgyzstan, Tajikstan, Afghanistan, and Pakistan.
And let me remind you the later is a known nuclear armed state, and the other is considered the Graveyard of Empires for very good reason, not even the US can deal with poorly armed combatants there.
This is not to mention that Afghanistan, northern Pakistan, and Kyrgyzstan are enormously mountainous countries, northern Pakistan itself is protected from China by some of the hardest to cross parts of the Himalayas. There's also only
one road between the countries, and when fighting in mountain passes, army sizes no longer matter. See battles like
The Battle of Thermopylea where a small Greek force managed to hold at bay at significantly larger Persian force for two to three days but then not only do that but to kill a disproportionate number of Persians than they themselves, this is the battle that became famous in the graphic novel and movie 300.
A similar rule of thumb applies to instances like the Swabian War that made Switzerland independent, because the much larger forces of the Hapsburg Holy Roman Empire and its allies had to claw through the Swiss Alps and you get plenty of instances where small bunches of plucky Swiss Alpiners face off against German forces that are sometimes two-times larger than their own, and then the Swiss win. The Germans don't get the maneuverability needed in attack phases and every time they sally out they get thrown into a grinder.
To quote from a 19th century source on warfare on this subject itself:
"For smaller bodies of troops, the disadvantages of a defensive position in mountains diminish as we have already remarked. The cause of this is, that such bodies take up less space, and require fewer roads for retreat, etc., etc. A single hill is not a mountain system, and has not the same disadvantages. The smaller the force, the more easily it can establish itself on a single ridge or hill, and the less will be the necessity for it to get entangled in the intricacies of countless steep mountain gorges."
clausewitz.com/readings/Compare/OnWar1..I have also heard it said - though I haven't found the source yet - that one man with a rifle in a mountain pass can hold off a significantly larger force (10 times more or so of his number) for a long time before he's finally beaten.
Numbers mean nothing when the bulk of your army has to make it through these obstacles. And in the mountains bombs and shit mean nothing when the enemy fighters can go into the natural bunkers of caves and wait out artillery strikes.
Beyond simple military tactics, you also ignore the geopolitical issues in blatantly invading 2-5 countries near to much stronger countries than those. Iran/Persia would have a lot to say about that, and would be threatened by a Chinese nation suddenly flooding in west to them. Even if you were to obtain an alliance with the Iranians the understanding between the parties would be by default that no superior edge is had over the other in invading this countries and if China were to invade this countries the alliance would be void in favor of forming a resistance to Chinese aggression and slowing or stopping Chinese growth.
But Iran isn't the only force to worry about either, you also have the equally powerful Indians in the region who given the same scenario would sure as hell hate it if China were to just up and one day take over their western neighbors and precious Kashmir. And India is a nuclear armed state too. If they believed it was necessary they could combine the stockpiles with Pakistan and basically nuke the Khunjerab pass to destroy the Chinese force crossing over or even go beyond to destroy Chinese staging grounds and cut the connection between you and your forces on the move.
The thing that's really an issue though is the merit of being a Roleplayer. As a GM you actually have a lot more pressure on you yourself to set an example. More so as such a large and notable power. If you start willingly and openly sweeping up large tracts of territory in the matter of a single post then that threatens the rest of us. And in an RP where you said we can have giant lasers cannons that take months to charge, then in invading those five countries in one post, and defeating a six-month Mongolian rebellion in one post really voids that statement when I can still charge and fire that same weapon in one post or two because that's just the sort of example you set.
You may be the head-honcho, but we keep the RP alive. If anyone feels they're not having fun because the GM is being in his own way abusive through power-playing, all excuses aside then we can just leave and your RP will die.