What if Alexander the great invades China

I think that the Qin will kick Alex's ass since the Chinese had gotten at least two thousand years of military history at the time of the Spring and Autumn period there are like over a thousand military tactics and Alexander only depends on numbers and formation he won't matched

If Alexander use 300,000 troops the Qin can wipe it out with 50,000

Remember Qin Shi Huang Di was one of the most brilliant military leader in history and the Qin got a good economy

"Alexander...only using numbers?  May I remind you that his (circa) 35,000 men defeated a Persian force of about 50,000 at Granicus, then about 150,000 at Issus, a similar force at Gaugamela, then, with about 50,000 men he defeated a similar force at Jhellum (Hysdaspe). 

I doubt that any Chinese general could match Alexander for military genius - as no general, until those who used the tactics which Alexander inveted, could improvise as quickly, and as effectively as him."

Do not compare the state of Qin to the "inferior and barbaric" Persia known in China. Alexander did not invent military tactics. The Chinese had their own versions of military tactics far more sophisticated and advanced than Alexandar's especailly after a thousand years of conflict and war between different feudal states. Wu Ji Sui's Wu army defeated Chu's army of 300,000 with a force of 100,000 is one of the thousand examples of winning a battle that ur outnumbered. China, by that time, already had different versions of war manuals and tactics developed and put in books as records and reference.

China also had superior military technology such as the seige weapons (i.e. cross bows) while Alexandar, on the other hand, only had arches, infantry, and calvary.

In terms of military tactic,s the chinese were definitely more advanced.

For example, there were tactics of beauty, pyschological warfare etc that the west had not heard of.

Sun Bing, Sun Zhi, Wu Zhi Sui were all military and tactics experts better than Alexandar. Ancient Chinese military not only relied on tactics during battle but also strategy and psychology. Along with Chinese's superior technology. Alexandar was no match against China. The Qin state by that time already had steel technology that could produce long and steel swords and weapons. Alexandar's force used short iron swords that were not match against the Chinese steels.

The Qin state could easily defeat a combined force of Alexandar and the Persian military. And, that's only one of the seven major states of China. The State of Chu, Chi, and Chin were all so powerful that each of them could deploy an army of 300,000 plus and other smaller states could deploy an army of 100,000.

The Chinese was technological superior, they outnumber the Greeks and the Persians, they had sophisticated war manuals and military formation as well as structure, they were experts in military strategy not limited to tacts during battles.

on the other hand, the West (including Alexandar and Persia) mainly focused on the tactics during battles and had inferior technology.

How could they win?

The Qin state had a standing army of 700,000 while conquering other six kingdoms.

"The same army which was destroyed by the 'barbaric' armies of the north centuries later? "

The barbaric force that conquered China was the Mongols, and it happened some 1500 years after the Qin. What does that have to do with anything? The Mongol also obtained firepower, cannons, and fire armed when capturing Northern China. They then applied this technology to its westward expansion, which went all the way to Europe.

"I've read Sun Zu (well parts of it..it was extremely obvious and dry), and if that's what you mean by strategy of war, "

Sun Zhi once stated "anyone could read the war manual but not everyone can get anything out of it. The knowledge behind the manual has to be interpreted by one that's talented about it. The war manual is not a dead thing to read but an area that one needs to explore." All Chinese generals read the war manual but not everyone was good at using it. But Sun Zhi, Ng Zhi Sui, Zhu Gor Lian are all some examples of famous tacticians. Pschological warfare was common in China during that time while it was unheard in the west in the same time frame.

"An army of that size presents numerous problems.  The logistical problems of fielding an army of that size in any one location is impossible, even for the Qin.  I also doubt that that army has been worked on by historians of today - you probably took that from a source, which most probably inflated the numbers.  In any case, the Qin would have probably only been able to field an army of 200,000 or 300,000 (using those numbers) against Alexander, and Alexander had a history of defeating enemies of that size - with considerable ease."

The Qin deployed an amry of 500,000 when conquering the state of Zhao. And, the feudal states frequently defeated a large army of 300,000+ throughout the history of spring and autumn and warring state. The Qin also executed an entire Zhao army of 400,000 after the Zhao army surrendered.

"On top of that, Han success in Vietnam and the Korean peninsula, as well as against the tribes of the Steppes, was very limited, and many times did poorly - and I doubt the Qin's were much better than the Hans."

Who said they did poorly? Han was the most powerful empire on earth of the time. It also defeated the Huns in the north. The Turks in the west. The Muslim region of north western China today was first conquered by the Han in Ancient time. And the rest of the west (central asia), Korea, Japan sent tributes to the Emperor in return of military protection.

"Most likely Alexander would have been able to ally, or at least guarantee the neutrality, of the other six Chinese factions, which would have only added pressure on the Qin's borders, forcing them to keep men on guard on those frontiers, severely limiting the amount of men he could have switched to fight against Alexander.  "

What makes you think the Chinese would ally with the Aliens they considered as being inferior and barbaric? The Chinese feudal states, although constantly fought against each other, did ally from times to times to launch campaign against barbaric tribes such as the Xiongnu (huns) in the north.

"In short, I would foresee a Macedonian victory."

A combined force of all the rest of the known world would not be able to defeat a combined forced of all the seven feudal chou states at the time due to tenhnological inferiority and lack of productivitiy. The Qin soldiers used steel weapons while Alexandar's soldiers used iron weapons. The Qin soldiers used crossbows while Alexandar's soldiers used archies. The Qin soldiers had sophisticated seige weapons that've been modified several times throughout the history of Spring and Autumn and Waring States while Alexandar came up with some seige weapons designed by himself. 

Besides, there was no large-scale contact between Chin and India due to the terrain and mountains that seperated them. The first contact was made during the Han dynasty. Buddhism didn't spread to China until the age of division, some 700 years after the Qin. The Indian version of warfare was completely different from China's.