Why didn't the wildlings go to another part of teh wall? it's 300 miles long why go there? Why not go specifically JUST there if they're trying to just get over into the south?
The gate would be the most vulnerable spot even though it was a extremely strong gate it is only the entrance. It took a mammoth and a few giants to even get that gate open. That is why Jon sent them to hold the gate.
I never read the books… but here’s my conclusion.
The Wildlings are a nomadic culture. They travel around quite alot.
IIRC, Mance Rayder mentioned in an episode in season 3 that every time they ‘settle down’ somewhere (for any extended period of time)… people in his camp start to turn up missing. Or some return as zombies. (or something to that effect, I can't remember the specific quote.) So they just keep it moving to the next location.
Anyways, Mance suspects the White Walkers are picking-off his Wildlings. Little by little.
Plus, in that same episode someone mentioned they were constantly sending out ‘scouts’ to investigate, but they never returned either.
And he does not have a ton of Worgs at his disposal to see what the hell is going on across the countryside.

(Pretty sure Jon Snow killed their VERY LAST Worg during his escape at the end of season 3

)
So he wants to move ALL those wildling tribes very far South of the wall, before “the long winter” arrives and an all-out war against the White Walkers pops off.
Remember, the Night’s Watch would NEVER allow all them Wildling’s to just waltz across the border, like that shit was some kind of medieval ‘customs checkpoint’.

No way. Absolutely not.
Their ONLY job is to protect the 7 kingdoms from EVERYTHING that is on the other side of the wall.
So The Night's Watch would sooner kill them ALL to prevent them from entering the North... mainly because of all that MAYHEM the Wildlings tend to pack in their luggage, to surprise unsuspecting townsfolk with.
So how does Mance & his tribes get across??
There are only 3 castles left with tunnels into the North, guarded by the Night’s Watch. (see map below)
- East Watch by the Sea (on the East Side)
- Castle Black (in the Middle)
- Shadow Tower (on the West side)
Apparently, Castle Black is the only place that Mance & his horde can cross easily, because they have a LARGE GATE. Not just tunnels. (And I think the other 2 castles are abandoned

)
If so, Mance couldn't go to any abandon castles because all the passages through the wall at abandon castles are most likely sealed up tight with boulders, rocks, debris and ice, just like Jon Snow suggested. (Because the Night’s Watch would never leave any passages wide-open at abandoned castles, if nobody was guarding them.

)
Also, Mance & his followers can’t just climb over the wall with 100,000+ men, and all those giants n shit, it would take too long and it's way too risky, and the wall is probably booby-trapped also. (like we saw tonight) And unstable as hell.
Plus they don’t have ANY ships to carry the 100,000+ men of the wildling army. So they can’t just sail around the bay at East Watch. (Otherwise, they probably would have done it a long time ago, if they could.)
So Castle Black is the #1 option.
Because they have gates & large tunnels that everyone can just move through (even on horseback) to get to the other side. (And them Frost Giants could always perform a little on-the-spot ‘re-construction' to make it a little bit wider, to send their Wooly Mammoths thru it also.)
So Mance knows… the only way to get South… is BY FORCE.
Right through Castle Black.

And the entire forces of the Night’s Watch.
So he will fight them all to the death, if need be.
question for the fam? How did Bran Stark get to the other side of the wall?
As Jon Snow was escaping from the Wildings, Brandon was hiding in a nearby abandoned (windmill) tower near Castle Black.
The Wildling Worg heard Hodor whimpering during the Thunderstorm, but Tormund just dismissed the noises as just 'ghosts', since the tower looked like it been abandoned for several years.
Sam told Gilly he read some of the books in the library at Castle Black that explains different ways that the tunnel systems lead into the North.
After he killed the White Walker, Sam & Gilley found an entrance to the tunnel system that led directly to the same tower that Brandon was hiding in.
So, Sam led Brandon right back the same way he came from the North, before heading back to Castle Black at the end of season 3.
I'm confused as to Mance's meaning for 'the largest fire the North has ever seen." I thought that was the singal that he would be bringing his entire army over the wall. The Night's Watch just barely survived the night. If Mance had just brought about 200 more guys and a couple more giants, he would have had that shit.
He should have approached that shit like Stannis did during the Battle of Blackwater. I forget who said the line, but someone told Stannis that storming the gate head on would lose them hundreds of men, and Stannis replied, "no, thousands." Stannis was ready to throw as many men to the fire as needed to get the victory.
Mance's WHOLE ARMY could not get over the wall.

(^^ see above for a few reasons)
That would be impossible.
The climb takes a few HOURS. And the ice is not stable.
So you can't send too many people up the side of the wall (at the same time) without creating an avalanche.
So Mance sent a small battalion of men (led by Tormund Giantsbane) over the wall a few days earlier... to pillage Molestown & cut off Castle Black's lines of communication.
In the final episode of season 3... he tells (red-haired) Tormund... "Have your Worg send his hawk over the wall every night to watch for my signal... I will light the biggest fire the North has ever seen."
The fire was a signal for Tormund and his squad to attack Castle Black from the OTHER side, at the same time.
Really this first battle was Mance testing the defenses of Castle Black.
Because he didn't know for a fact exactly 'how many' men were guarding it.
So he sent his first 'assault team' in to find out.
He could've lost every last frost giant he had if those fire barrels got dropped on all of them at once, as they tried to break down the gate.