Was it ever possible to take successive castles by surprise? Or completely ignore them and move on through enemy land? We see the Blackfish holding out against the Lannisters/Freys with just 200 men, but at the start of the war, the westerlands armies rampage all across the Riverlands incredibly quickly, and Twyin after the Green Fork somehow takes Harranhal by walking in. Is this just off page weirdness?

Yeah, that particular part of the campaign has GRRM’s thumb squarely on the scales, because it has to happen that way in order to set up Robb’s decision to go for Jaime or Tywin.

I mean, it’s technically possible to take successive castles by surprise – but it becomes increasingly unlikely with each castle, because word spreads fast. And it’s absolutely possible to ignore castles as long as you’re willing to live off the land and cut yourself off from supply lines, but that doesn’t seem to be what Tywin was doing, since these castles are described as fallen not bypassed.

As for Harrenhal, that’s never made sense.

While Jon focusing NW on archery is a good idea now, was it really bad for NW to focus on melee weaponry prior to start of the story? Horde of Wildlings attacking the wall is a new development, so likely 99+% of wildling encounters happened on Rangings and the like, where melee is more useful. In addition, practice shooting at horizontal targets 100′ away or so is of marginal benefit when shooting at enemies 700′ directly below you.

One important corrective: “hordes of wildlings attacking the Wall” is NOT a new development:

“Wildlings have invaded the realm before.“ Jon had heard the tales from Old Nan and Maester Luwin both, back at Winterfell. “Raymun Redbeard led them south in the time of my grandfather’s grandfather, and before him there was a king named Bael the Bard.”
“Aye, and long before them came the Horned Lord and the brother kings Gendel and Gorne, and in ancient days Joramun, who blew the Horn of Winter and woke giants from the earth. Each man of them broke his strength on the Wall, or was broken by the power of Winterfell on the far side…”

The Watch is primarily a defensive military force manning a fixed fortification. GRRM’s problems with math aside, it makes a lot more sense to train them in archery and siege weaponry than it does to emphasize hand-to-hand training, given that melee weapons’ arms-length range doesn’t do you much good when you’re on the top of a bloody great wall and the enemy is at the bottom.

Now, ranging is a different story, but I would maintain that Ser Alliser’s godawful training scheme is still a bad one: emphasizing fighting on foot one-on-one is a very bad idea when the Night’s Watch is badly outnumbered by wildling raiders, who are absolutely going to use their advantage of numbers to overwhelm whatever negligable training in the blade a crow gets in boot camp.

To the extent that you’d emphasize melee combat at all in the Watch, it should absolutely be focusing on cavalry tactics, which would allow the Night’s Watch to punch above their weight vis-a-vis the mostly on-foot Wildlings. And cavalry tactics emphasize horsemanship over swordsmanship, because you don’t need to be very good with a sword when you’re thundering down on someone at top horsepower.

Pegging Westerosi technology at mid 14th century – early 15th century depending on location (mail and leather in some places, full plate and armored horses in others) but with a total lack of gun powder. Assuming gunpowder never appears where does military technology and tactics go in the next 100 years? Woud a Renaissance with out gunpodwer resurect roman tactics? Also assuming the others don’t knock them back to the dawn age

That’s a great question! Without gunpowder, you’re not going to get the same movement from medieval armies focused around knightly charges to the pike-and-shotte tactics of the Early modern era, so you’re going to see a different development pattern.

In the short term, I think the Golden Company’s model of combined arms and disciplined infantry is going to become dominant once someone realizes how much there is to gain from upgrading the quality of Westerosi infantry and having them work in concert with the cavalry rather than independently.

You might see cavalry tactics shift somewhat if the Dothraki have a big impact on Westeros, similar to how the Byzantine cataphracts adopted the horsebow and hit-and-run tactics from the Huns, the stirrup from the Avars, etc. Westerosi knights are pretty damn effective already – if you could train them to use composite bows, you’d have a really frighteningly effective force on the battlefield.

And eventually, someone’s going to figure out how to make an effective repeating crossbow with a decent range and penetrating power, and then you’re likely to see a different kind of pike-and-shotte tactics: