Ned studied history of the North but the North doesn't exist in isolation, even before rise of Targaryen dynasty and in times when the North was an independent kingdom, it had interactions with other Kingdoms, so studying the North's history meant studying history of all Seven Kingdoms. His study lead him to a fundamental conclusion, everyone wants to survive and thrive. Of course Ned has always known this, it is basic human nature after all, but he didn't understand just how many human interactions boiled down to this basic human desire. Ned has often wondered about the Game of Thrones these Southrons always played. Why do they so desperately want more and more power? Why do they act dishonorably, lie, cheat and murder for it? Now he knew, it isn't just enough to survive, humans want to thrive, hadn't he himself wanted House Stark to prosper and to grow stronger? The North always had to struggle to survive, if the North is as plentiful as the South, what guarantee is there that the North won't just be like the South, what guarantee is there that the northern lords won't play this Game of Thrones ? Ned realised that there is none. Somehow that thought made Ned despondent and melancholic.
But those thoughts were irrelevant to the matter at hand. What are the threats to the North?
The greatest threat would be Winter. Solution to that is simple enough, more grain and preserved food stuffs, better insulated homes. The food issue is being taken care off, gold from Ironwood and Wintersteel should be coming in soon that meant ability to import more food. Ned should probably suggest to Father to expand granaries for more storage and expansion of glass gardens for greater variety and availability of vegetables for Winter, but constructing those will cost gold, which means less coin for food imports. If House Stark wants to decrease import costs alliances need to be made, those are usually sealed with marriages. Only Kingdoms who can produce excess grain to export it are Riverlands and Reach. Reach Lords probably won't be receptive to idea of marrying their daughters to 'Northern barbarians', not enough benefits for them and transporting the grain will cost exorbitant sums, that leaves Riverlands, from whom North already imports a lot of grain from. An alliance should be with either House Tully or House Darry, House Darry because of the vast fertile lands they have under their control near Harrenhal, but they don't have marriageable daughters available, that left House Tully, Lord Hoster Tully has two daughters, eldest of whom is an year younger than Ned and an infant son. But riverland lords are a fractious lot and Lord Hoster will expect the North's support in event of conflict breaking out, either due internal threats or from any external threat. Afterall whenever Seven Kingdoms go to war Riverlands burn. Lord Hoster will also expect Brandon as the bridegroom for one of his daughters, this is simply not possible, House Stark is going to ruffle alot of feathers in the North in next few years, if Northern Lords find out future Lady of Winterfell is going to be Southron, it will displease them even more and Northern Lords aren't very subtle at showing their displeasure either. So either Ned or Ben will have to marry one of Lord Hosters daughters and Ned has a feeling that Lord Hoster won't make it easy, he would try to insist on Brandon but he would have to settle for Ned or Ben. Then the issue of loss of life due to cold, the Norths smallfolk need better protection against the cold, maybe better homes and better clothes, but Ned didn't have any knowledge in that field. Maybe Wildlings are the solution, they survive in harsher cold beyond the Wall, maybe they know some tricks to surviving the cold?. Ned will put these two ideas in his next letter to Lord Father, he will know what to do.
The second biggest threat to the North would be Wildlings. For that there is already a solution, it just isn't working due to neglect. The Night's Watch needs to be strengthened to put a stop to Wildling threat. Wildlings aren't even that successful in their raids. Nine out of ten Wildling raids end with all of the Wildlings dead eventually before they can cross back to beyond the Wall, but before they are dead they wreck havoc, slaughtering smallfolk, torching fields and villages. If the Nights Watch can properly man the Wall Wildlings won't be a threat. There are already plans in motion to strengthening the Watch and Ned doesn't have any new ideas, so this issue can be put aside for now.
Third greatest threat to the North would be the Ironborn. They are a menace. Murderers and rapists that they are, they semi regularly raid western coast of the North and the Bear Island. There used to be several fishing villages along Stony Shore and near Sea Dragon Point, Ironborn raids have resulted in desertion and destruction of those Villages, now there are maybe two or three villages there. The Norths fortification of its western shore is a necessity. Just a single castle at an appropriate place near the coast can put a stop to any ideas of an invading the North through there. Having no military presence there is a mistake and one that, Ned fears, will bite them in the ass if not corrected in a hurry. Whenever a war breaks out in Westeros Ironborn scum reave without fear of consequences, why should they fear, when fighting men are busy elsewhere, after the war is done they slink back to pile of shit stained rocks they call home and Lords and smallfolk will be busy rebuilding after the devastation left behind by War for any meaningful retaliation. Whoa, Ned never knew he hated Ironborn this much, anyway Ned will think on it some other time. So the North needs to secure it's Western coast, best way to do that will be by building a Castle and having a strong garrison in said Castle. Maybe, Ben can be given Lordship over said Castle? . If possible build a fleet , but building a fleet has its own difficulties, building ships is already a costly endeavour, but then there is a need for experienced captains and seamen who can train newer sailors. Ned will write about this to his Father too. Ned really hopes those prospectors will find something worthwhile, all of this is going to cost substantial amounts of gold dragons.
Fourth significant threat to the North would be House Bolton, specifically if they ever rebel against House Stark and have enough support from other Houses to oust or extinguish House Stark and take control of the North. House Bolton would be a disaster for the North, it isn't that House Stark has been a paragon of virtue in the past, House Stark has been as brutal if not worse than House Bolton, somethings his ancestors did make Ned break out in cold sweat even now, it's that in past near eight thousand years of existence of their House, near as old as House Stark, House Bolton didn't seem to have learnt that being feared is only a part being a successful ruler, being respected and loved is another major part of it. If House Bolton ever gained the North they will be ousted in less than five years, but those five years would be a disaster for the North. So House Bolton needs to be under very careful watch, and House Stark needs to be ready to stomp down on any stupid ideas. This issue will be taken care off when Brans idea for the spy ring takes off.
That leaves final and fifth significant threat to the North, an invasion from the South, something must go very very wrong indeed for that to happen ,like the resurgence of Faith Militant wrong or the King going mad wrong, at that thought Ned shivered, he dearly hoped he didn't jinx himself. Part of the solution for this problem is Neds fostering at Vale, if Ned made meaningful and strong connections while he was in the South, it will nip any such problems in the bud. Securing the North's coasts and rebuilding of Moat Cailin will make any thoughts of invading the North a very very foolish notion and a impossibility. As Lord Father already indicated Moat Cailin will be reconstructed and Ned will take Lordship over it, this potential problem seems be well on the way to be taken care of.
It seems Ned has to write a long and sensitive letter to his Lord Father, once again Ned thanked Brandon in his mind for his brilliant idea of encoding letters.