Well, I can answer this question from a specifically Tudor-Stuart English (and semi-British) perspective.

At the time, the primary way hose was held up was with garters, which were either ribbons of tied fabric with the knot facing backwards, or in the case of more fancy one like the Garter order garter; a metallic jewellery band. Hose is really stockings more than socks though, it must be said. Modern stockings are essentially hose, which would be why stockings for women survived since women's fashion did not develop pants. Earlier hose were one piece and could be attached to the tunic, but in the Tudor-Stuart period hose was separated into the lower hose which reached just above the knee, called netherhosen or "Venetians", and cannions which covered the upper leg. The lower hose were more important since they also wore trunks, breeches or skirts which covered part of the upper leg.

Breeches are the longer, thinner one (originally specialised for hunting) that became dominant from the mid-17th century up until trousers. Whereas, trunks were the older fashion where you get the "pumpkin pants" with a puffier shape and panes. More in Elizabeth's I's time. Interestingly, the early-Tudor fashion around Henry VIII's time for men's skirts was retained seeming longer for poorer peoples, a common trend in historical clothing and in this case perhaps furthered by the fact that skirts were cheaper and less cumbersome than wide padded trunks. See for example this one from c. 1568 https://commons.wikimedia.org/wiki/File:Pieter_Bruegel_the_Elder_014_detail1.jpg and this one from as late as c 1594 https://commons.wikimedia.org/wiki/File:Gardeners_1594.jpg

Underneath these, they also had drawers, which would take another century or two to pass into use in women's fashion (!). Women had to make do with hose and layers of skirts, which did work well and maybe made it easier to poo into a chamber pot, so it wasn't all bad.

Sailors at the time however, sometimes wore striped trousers, which were probably fastened with a belt if necessary. That would also be the kind of active working environment were skirts were seen more often.

Tunics disappeared because they were replaced by doublets, which were not quite as long and worn with trunks, skirts or breeches. And then the doublet was replaced by the justacorps and waistcoat in the later 17th century combined with breeches and neckcloths replaced the early-17th century wired collars.

In terms of how trousers evolved (modern pants), breeches in the early 19th century got longer and hose became shorter until pants were standard by around the 1830s. Shoes also got somwhat more covering at the ankle corresponding with this, many mid-to-late 19th century shoes are dress boots. And 19th century underwear became slightly bigger than earlier men's drawers. Similarly to how regency coats became modern suits, although that process is more convoluted and multi-ended.

Well, it may be a drawback to your search that reenactors focus on the period they're reenacting, but another part of the problem is that there is no single answer for how all legwear worked up until the nineteenth century.

In the later Middle Ages, hose was sort of like really long socks ... but in a way, more like pantyhose. Earlier in the period, hose was just stockings, held higher up on the leg with garters; above them, men would wear essentially loincloths. You can see the loincloths in the slits of agricultural laborer's shirts in the June and July illuminations in the Duke of Berry's Les Très Riches Heures, ca. 1415: in the heat, they've taken off their outer upper-body garments, and in many cases removed or rolled down their hose.

(Not totally necessary to this explanation, but worth mentioning: hose was generally made with woven fabric, cut on the bias - that is, diagonally to the weave. They wouldn't conform to the body the way a modern machine-knitted sock with elastic spun into the thread will, but the bias would let the fabric stretch and fit relatively closely for a non-spandex world.)

As shorter upper garments became the norm for men in the mid-fourteenth century, however, it was necessary to conceal the upper thighs and parts adjacent. Hose was constructed to come all the way up to the hips, where they would fasten with small ties to the waist of the doublet, and with shaping and seaming around the back. These would not be sewn together at the front, though. Instead, the Personal Area would be covered with a flap that also laced to the doublet at the top. This flap, which could be a handy pocket for the storage of small things, would become shaped and padded - the codpiece. (You can see the changed situation in the July image from the Hours of Charles d'Angouleme.) By the end of the fifteenth/beginning of the sixteenth century, these were of course fashionably massive. Underneath these tight-fitting hose, men could simply tuck their shirts between their legs, but some would wear drawers, tiny shorts of linen held up with a drawstring.

It's also important to note, to bridge the gap between this answer and /u/Somecrazynerd's, that hose also became split around the same time into upper hose and nether (lower) hose. The bottom halves of the hose went back to being what hose was previously: stockings held up with garters. People would develop various styles for the upper hose, some fuller and some tighter, still with the codpiece covering the opening between the sides.

At the beginning of the seventeenth century, upper hose would be worn rather full and the codpiece was pretty well phased out in fashionable contexts. It became normal for these breeches to be simply hooked to the waist of the doublet, rather than laced, and for them to button shut in front. Something like the codpiece would return in the mid-eighteenth century, as the front-buttoning opening was replaced with another flap, called a fall, that would come up and cover the front, buttoning to the waistband. This would remain common into the early nineteenth century, even as the breeches lengthened into trousers, and then we meet up with the period that you understand already.