Quote Originally Posted by AqD View Post
1) They were not an unified kingdom and have no intention to launch a large-scale invasion.
They did launch a large scale invasion, though. At the end of the fourth or beginning of the third century the Sarmatians moved from the Kuban region across the Don and into the region between the Dnieper and the Don. Within a century or two they reached almost to the Danube and had a strong foothold on all the land between the Don and the Dniester, with the exemption of most of the Crimea, of course.

2) Their preferred tactics is not very useful against forts or walled cities.
3) Even if they're unified and beat settled people, they cannot maintain the army & combat style once they settle and become farmers and merchants. This would limit their further expansion.
These points are largely irrelevant. The Sarmatians, and many other nomadic peoples, managed to defeat and subjugate major cities despite not employing siege tactics. The Sarmatians did intermingle and settle with the Greeks of the Bosporan kingdom, but they largely employed the standard nomadic method of maintaining a subjugated empire: they forced cities to be aligned with them and to pay tribute.

4) They were hired as mercenaries by various factions, even oppositing ones. They're not one kingdom or one people so the word "subjugated" is not really accurate.
They were separate tribes, but they certainly worked in unison, or at least we do not hear of major conflicts between Sarmatian groups. Whatever the political situation within the Sarmatians themselves, the result was clearly a migration of Sarmatian tribes moving in unison that appeared to be a tribal confederacy to outsiders.

5) Their bows are certainly superior to western hunting bows, but not really better than other eastern ones. Since nobody would seriously consider western bows as a real weapon, this "advantage" doesn't matter. (BTW roman auxilia archers were using Scythian bows)
Their bows were basically the same kind as used by all eastern peoples in this time until the introduction of the "Sassanian" bow, but this can be brought back to the general state of nomadic warfare at this time.

I think the real reason that the Sarmatians did not invade Europe and wreak havoc is because, like the 'Royal' Scythians before them, they were content to control the northern Black Sea littoral and had much to deal with there anyway.

When you ask why they didn't continue their movement into Europe, you're also forgetting the reason that the Sarmatians moved westward in the first place - they were pushed out in one of the great steppe "domino effects" of history. They basically seem to have been pressured into moving west from the Urals to the Kuban region and then finally into the northern Black Sea littoral rather than invading westward of their own initiative.