This is a misconception over the resolution of Midieval European sieges. Storming fortificatins were extremely expensive due to lack of gunpowder artillery, so it wasn't done very often. The vast majority of the time sieges were resolved by starving out the defenders.Yes, there is a point to raising a huge offensive field army, because if you don't, you won't be able to overcome the defenders in their force-multiplying castle.
In that scenerio having a huge army...doesn't actually help that much. Once you cut off the roads etc there's not much they can do to make the defenders starve out faster. In fact, having a bigger army made things more -difficult- for the attackers: since now you have to provision your army for very long extended period of time and you have more mouths to feed.
Sure, but it's still much, much smaller number of men than big field armies. A few hundred men can garrison fortfications capable of holding out against many times their number.Similarly, by raising more men on the defense, you can insure yourself against one of your forts falling to a superior enemy by having more forts, allowing you to better dispute more territory.
Yeah sure every general always wants a million men but warfare are constranined by economics.To put it plainly, numerical superiority has always been an advantage of fundamental importance, to be sought everywhere to the greatest degree possible. Any theory positing there was a time where this wasn't true is pure sophistry.
Yeah you want to have a huge army but you probably dont' want to pay for it. If you can have a few hundred men holding a castle against 10x their number, why are paying more men to sit around? In economic terms their marginal value drops singificantly, while their marginal cost doesn't. Fortifications fundamentally alters the cost effective configuration of your armies. Once fortifications fell more easily then yeah you have to get bigger field armies but the cost of those were often ruinous, unpaid soldiers marauding through a countryside were a frequent feature of both medieval and early modern wars for a reason. If you can pay a few hundred men to hold a fortification cheaply then there's no point in shelling out the cash for 10x when their value doesn't justify the cost.
Yeah I'm not saying long expensive sieges or assaults never ever occured, I'm just saying the proportion of them changed. Now taking fortifications are much easier than before. Im' not saying sieges stopped being important, I'm just saying that the emphasis shifted onto field armies more so than before.Moreover, insofar as this was ever true of the medieval era, it's just as true for the early modern period. Lots of early modern sieges failed or dragged on forever or took grievous losses. Metz defied Charles V even after the walls were breached. Ostend held out three years, Candia for twenty one, and Ceuta for 26. Perhaps 20,000 Ottomans died before the walls of Malta, Famagusta, and Tunis. Even after Gustavus Adolphus was killed at Lutzen and his army smashed at Nordlingen, the extensive fortifications Sweden still held ensured they retained large German territories.