Failure of the Andals on Essos

[Toccs]

Or maybe Prince Garin's famous battle with the Valyrians was actually a noble sacrifice in order to distract the dragon lords while Nymeria escaped with the bulk of their people.

[Tommen]

Valyria went to war with the Ghiscari Empire (and thus rose to power) five thousand years before current events. The Andal invasion might have been as long ago as six thousand years before Aegon's Landing (although this isn't certain, I believe). They might not have been powerful enough to have much of an influence on Essos, but they were up against the several sovereign kingdoms of the First Men and, as Robert Baratheon so eloquently once demonstrated, one united army can often be more effective than five disparate ones. I believe the Andals were more technologically advanced too, taking metalworking techniques they learned from the Rhoynar to forge superior steel weapons. And, as we know, they weren't able to subdue the North at all.

[OldManDennis]

I would guess the Andals came over more like the Germans to Britain, rather then the Normans. Which is to say they came over gradually in waves, each group pushing farther west and north looking for good lands and suppressing displacing locals as they go. Eventually the technology and military ideas they brought are going to outpace the colonists and the natives will be able to resist. Think of how Scotland and Wales are more able to keep their British culture then England, where the Angles and Saxons took root.

[AzureOwl]

Looking at the map of the regions north of Valyria and east of the Forest of Qohor one can see how Valyrian expansion might have triggered the Andal migration long before any Valyrian ever set foot west of the Rhoyne.

If the Valyrians moved north over the Painted Mountains into what is the today the Dothraki Sea, that could have prompted whoever was living there to move west into the hills around Essaria, starting the domino effect. The people living at the time in those hills would’ve been pushed into the Forest of Qohor, displacing its inhabitants northwest into the headwaters of the Darkwater. The Rhoynar appear to have already been more advanced than the Andals at the time, so the path of least resistance would’ve been for the dominos to move further northwest, pushing whoever lived in the Hills of Norvos at the time right into Andalos. With their backs to the sea, moving Westeros would’ve been the likely outcome.

[Dorian Martell]

Illyrio tells Tyrion that the Andals learned to forge steel from the Rhoynar. The first men on Westeros only had bronze weapons. the Andals probably thought westeros was an easier target then the large Rhoynar empire. The Andals conquered or married into all of the kingdoms of westeros except the north, which seems too cold for anyone from Essos to conquer.