system
Given the following post, respond as if you're commenting on Reddit:
human
[ASOIAF] Why are the Seven Kingdoms afraid of the prospect of a Dothraki invasion when they outnumber them twenty to one?

It's mentioned in A Game of Thrones that Viserys Targaryen wants to invade Westeros with an army of "ten thousand Dothraki screamers". These are all light cavalrymen, of whom a single Westerosi knight, Ser Jorah Mormont or Barristan Selmy (who are very skilled, I'll concede) can make short work in single combat. While knights are a minority in Westerosi militaries, House Tyrell alone can muster 100-120,000 men, Lannister 60,000, House Stark several tens of thousands and so on, and all these militaries are sophisticated and diverse, with access to fortifications, advanced tactics, superior technology and ranged capability and so on. So why would such a massive, well-supplied war machine be afraid of such a comparatively small force of Dothraki, when even a single Great House seems like it could easily repulse an invasion, especially on their home turf?
gpt
Simply put, Viserys is wrong. He vastly overestimates his own abilities as a leader. Right after Dany tells him what Viserys says, Jorah Mormont snorts and says and says that Viserys "would not be able to sweep a stable with ten thousand brooms". There might be a few Lords that would join a Targaryen returned but even with their help it's all pretty much a false hope at that point.

So not many people in the Seven Kingdoms are afraid of a Dothraki invasion. The Dothraki have never attacked by sea and most people don't know there's even Targaryens still alive. Viserys dreams big but he's really just insignificant in the grand scheme of things. He's not smart enough, charismatic enough, or skilled enough to make his visions a reality.