system
Given the following post, respond as if you're commenting on Reddit:
human
[Game of Thrones] How do the Wildlings feed their army? (Spoilers)

The Wildlings have an army of a hundred thousand people. They're consistently cold and consistently on the move. A 2000 calorie requirement per person per day would be conservative.

The climate of the region beyond the Wall is far from conducive to farming. So far as I'm aware, in fact, the permafrost conditions make all but the most hardy crops unfarmable, which leaves meat and fish as the primary sources of calories. 

Venison from deer and elk has a calorie content of about 1440 kcal/kg. Salmon is a bit better, at about 2080 kcal/kg. So a Wildling would need to eat at minimum 1.5 kg of venison or 1 kg of salmon meat or some combination of the two per day. That comes out to about 150,000 kg of venison or 100,000 kg of salmon meat per day for the whole army.

A deer will yield about 25-50 kg of useable meat. More generally, a deer will yield about 65-75 percent of its living mass as useable meat. Salmon are about the same ratio, but obviously much smaller than deer. Your average salmon might be about 5 kg total weight, and yield about 3-3.5 kg useful meat.

To be generous, I will use the upper bounds of these ranges. So, 50 kg of meat per deer and 3.5 kg of meat per salmon. 

In order to satisfy the caloric requirements of 100,000 people, they would need to hunt 3,000 large deer, or catch about 28,571 salmon, or some intermediate of the two, *per day*. Given the climate of the lands beyond the Wall, I just don't see how that is possible. 

So: how do they feed themselves?
gpt
In warfare from the time of the Romans until the end of the 19th century, the army would not usually be assembled all at once. Instead, it would be divided into groups of several thousand, scattered across miles of countryside for this exact reason. Any group of substantial number is going to strip the land bare in a matter of days. This is even more true Beyond the Wall, where game is scare and crops are all but nonexistent.

This was part of why Mance made the massive signal fire. It's likely that his forces were scattered across the land in order to keep themselves fed. The fire needed to be able to be seen from miles and miles away. That's what it did.

In addition, a majority of those in Mance's army are not warriors. Rather, they are what we'd call "camp followers." Women, children. The old and the sick and the young. They're going to bring with them a menagerie of animals. Horses, chickens, goats, pigs, and other livestock. These people are also going to bring food with them, and feed and take care of the warriors as much as possible. If foraging is not enough, they butcher a pig and cook it up.

The siege of The Wall actually took days, as waves of Wildlings came in and reinforced those already at The Wall. Later, this exact issue is addressed as groups of Wildlings come in from the defeated force looking for food, warmth, etc. The largest group being that of Tormund Giantsbane, who brought with him approx. 4,000 Wildlings when he came over.