I took a history fashion class, but I am by no way an expert. Collars were usually made separate from the shirt, and could be washed, ironed and starched separate. In the 1930's, men's shirts began having the collar attached.

I'm an expert!

Ok, so basically, the first real shirt collars (as in a band of fabric that is attached to a shirt and wraps around the neck) started to appear in the early 16th century. It is commonly accepted in the costume history community that this was a natural evolution of the ruffle or gathered embellishment at the edge of a shirt neckline that started appearing in the late 15th century.

It goes something like this:

1493: Self Portrait, by Albrecht Dürer.

1508: Portrait of a goldsmith from Mechlen, by Dürer.

1516: Portrait of a Man, by Dürer

1521: Portrait of a Young Man, by Dürer

1525: Study of Anna Meyer, by Holbein the younger

1537: Charles I, by Clouet

1540: Henry Howard, Earl of Surrey, by Holbein the younger

1558: Mary Stuart, by François Clouet

1560s: Henri de Guise, François Clouet

1571: Claude Catherine de Clermont, by Clouet

And so forth until you end up with contraptions around the neck that need a separate support structure underneath to keep them propped up (called a suportasse) a'la Sir Walter Raleigh, painted by Hilliard in the late 1580s.

After the end of the 16th century, the ruff went through some dimension changes, but the collar remained, at least in terms of menswear. For women, high-necked smocks with collars fell out of fashion with the ruff, but were revived for hunting attire, which was based on menswear.

In an effort to keep this from getting too long, I'll stop there. Male dress never really abandons the collar, while female dress goes through phases depending on what was fashionable during any given period, or time of day, or occasion, right up until today.

Does that help give you some background?

Good question! I had never really thought about it before. Neither has anyone else, it seems, because I had to look at art to determine it, despite having Boucher and Waugh in my home library and Costumer's Manifesto historical pages online. It would probably have shown up in Hill & Bucknell's patterns, but I couldn't access that and my memory guided me to the right era.

Shirts were underwear, designed to keep the dead skin and skin grease off the inside of the actual garments. So they are rarely shown. However, if the tunic has a collarless neck, the shirt can't have one w/o showing.

Around the middle of the 1300s, Western European clothing had a revolution: the start of tailoring and real fashion with all its arbitrary and difficult trends. One development was the collar, whether a band on the fitted pourpoint or the ear-high arum lily collar on a houpellande. If you look closely you can sometimes see a narrow strip of white above the pourpoint's collar that is a narrow band collar on the shirt.

When fashion decrees an open front in the early 1400s, you can see this very clearly. On young Renaissance men wearing very open fashions, the shirt is cut down and that collar becomes a band across the chest to control the fabric.

In more conservative styles, like the best known portrait of Henry VIII, the band collar of the shirt has a ruffle. This will detach and grow into a monstrous separate ruff that is tied on over the band of the shirt. Finally, the ruff has to be supported on a wire framework.

Fashion eventually removes this, and it simplifies into the falling band seen on Pilgrims and other Puritans. It also expands into the cavalier collar you see in 3 Musketeers movies.

In the later 1600s this all goes away, doublets, ruffs, big collars. The French and English courts adopt the "Persian costume" of coat, vest, and breeches. The band collar is hidden by various neckcloths like the Steinkirk, but it's there.

In the late 1700s it starts to grow and become visible above the cravat. In the early 1800s the band collar is so wide that it wraps your head up to your eyebrows! Then you fold it in half, so it is around your jawline, and tie your cravat around it. The folded corners naturally bend down over the cravat when you turn your head.

This style continued until d'Orsay's coloured cravats became the early ties. The fashion for a wing collar resulted in a return to separate collars or bands, which single layer could be starched or even gummed to absolute rigidity. Some wings were so large that the Germans dubbed them "father murderers" that would cut your father's throat when you hugged him in greeting. Detachable collars fastened with collar buttons became popular in the US c. 1827 but took longer to catch on abroad.

Fold-over collars developed around the 1860s, by a look through Gernsheim's Victorian and Edwardian Fashion, A Photographic Survey. Sears Catalogs of the late 1800s devote a couple of pages to the different styles: fold-over or wing or just straight up, pointed corners or round, how high, how much cutaway.

Rich men could afford a band box full of starched laundered collars. The aspiring but impecunius market led to the development, in linen textures, first of white rubber collars then opaque white celluloid. Both stayed rigid and could just be wiped off to clean. Supposedly they were undetectable to the eye. There were also collars of fabric over cardboard.

This was the situation until WWI, as you can see in photographs. US combat uniforms were issued with shirts with attached, soft, foldover collars, because detachable collars always got lost. Men loved them after the years of stiff collars, and the British after the war decried them as another horribly casual Yankee imposition. The funny part is that in 1920 catalogs were selling detachable soft collars.

Now, I would like to point out that this is the conventional party line on shirt history.

However, shirts with attached soft collars had been worn for awhile, at least in the US. There was a specific woolen shirt worn, both by firemen in 1858 and later in the West (on John Wayne), with a panel front buttoned over a placket opening (Folkwear has a pattern for it if you want one). Gorsline includes it in his chapter on Western clothing.

The Army attached collar shirt would seem to be a hybrid of this flannel hunting shirt and the normal linen/cotton day shirt.

(I find this double-breasted shirt on page 531 of the Fall 1900 Sears catalog, as part of two pages of flannel shirts with attached soft collars.)

Tldr: shirts got a band collar in the later 1300s. The collar was very visible in the early Renaissance, then again around 1800. The shape of detachable collars was a major fashion statement for men through 1920. Then the attached soft fold-over became the norm, with wing collars fossilized in formal wear.