1.2 - further and farther, the Qin Dynasty??

[Connacht]

The establishment of the Silk Road shows that this geographical barrier that you seem to think existed between China and Iran/Bactria would not "make conquest impossible." It is, just like between Iberia and Bactria, a matter of distance and route.

A series of merchants that travel for a long time following some trading routes isn't the same thing as a huge army that enters the steppes for an invasion of a whole continent.
Unless your army is a nomadic horse horde and you are called Temujin.

You have a woefully limited understanding of Chinese history. The Chinese didn't just send "an army to defeat the steppe nomads."

You misunderstood my post. I wasn't saying that the Chinese didn't do any military campaign at all.

Expansion under the Qin and Han was enormous, including the Korean peninsula, southwest China and parts of Vietnam, and parts of the Tarim basin, an empire which is not insignificant when compares to the the Seleucids'.

And so? The Romans conquered Britannia, North Africa and Phoenicia, does these conquest make them probably invaders of China? Come on, you're telling of Vietnam and Korea, they are completely different countries, they are really closer to the heart of China than Europe and connection with them was really a completely different thing than an hypotetical connection with Mid-East or Eastern Europe.
The fact that a Chinese army attacked Korea is a story that has anything to do with a serious attempt of conquering the far West (or vice versa).

But, well, yeah, if the Chinese conquered even Southern China, then it's obvious that they could be able to reach the Mediterranean Sea. ;)

Arguing from a gameplay perspective makes little sense in this respect. You could argue from the same angle that it is not worth including the Iberians in the same map as Bactrians because, though they could meet, it is almost impossible to do so in an average game. The Chinese could meet Bactria, for instance, and that scenario is more likely than finding Iberians in Bactria (as shown historically in the episode described above).

A simple contact isn't enough for allowing a large-scale war scenario.
Bactria would have _a lot more_ things to do with Eastern countries than China could be with Bactria. And Eastern countries have a lot more in common with Western European countries.
Bactrians during the game may really make their presence visible to Seleucians and Parthians (and whoever could be there), while I don't think that a Roman/Greek/Seleucian player could notice a Chinese empire coming to knock at his doors because it wants to conquer Persia, Mesopotamia, Asia Minor and then go further: even if China should reach the territories that are today's Sinkiang and Tibet, distances would be too long from the mainland of China to lands west of Transoxiana.

I repeat what is my opinion: Chinese in game would remain in Eastern Asia doing their business, as well as Western countries would mind their own one. In a realistic mod, any attempt of a player to invade one side would be a logistical sucide (... if a player manages to make his dominions enough large during the timeframe) for the reasons said before. That's not a pic nic.