A stew is a common dish made of vegetables (particularly potatoes or beans), some fruits (e.g. peppers and tomatoes), meat, poultry, or seafood cooked in some sort of broth or sauce. The lines between stew, soup, and casserole are fine ones. Generally, a stew's ingredients are cut in larger pieces than a soup's and retain some of their individual flavours; a stew may have thicker broth than a soup, and more liquid than a casserole; a stew is more likely to be eaten as a main course than as a starter, unlike soup; and a stew can be cooked on either the stove top or in the oven, while casseroles are almost always cooked in the oven, and soups are almost always cooked on the stovetop. There are exceptions; for example, an oyster stew is thin bodied, more like a soup.
Stewing has a long tradition in cookery. Popular recipes for regional stews, such as gumbo, bouillabaise, Brunswick stew, and burgoo became common during the 19th century and increased in popularity during the 20th.
Written records of stews go back as far as written cookbooks. There are recipes for lamb stews & fish stews in the Roman cookery book Apicius, which probably dates from the 4th century. Taillevent (French chef, 1310-1395 whose real name was Guillaume Tirel) wrote Le Viandier, one of the oldest cookbooks in French; this also has ragouts or stews of various types in it.
To go back even further, there is ample evidence from primitive tribes who survived into the 19th and 20th centuries, that they could and did boil foods together (which is what a stew essentially is). Amazonian tribes used the shells of turtles, boiling the entrails of the turtle and various other ingredients. Other cultures used the shells of large mollusks (clams etc.) to boil foods. There is archaeological evidence of these practices going back 7,000 or 8,000 years or more.
Herodotus tells us of the Scythians (8th to 4th centuries BC), who "put the flesh into an animal's paunch, mix water with it, and boil it like that over the bone fire. The bones burn very well, and the paunch easily contains all the meat once it has been striped off. In this way an ox, or any other sacrificial beast, is ingeniously made to boil itself." (Some sources feel this was how some of the first 'boiling' was done by primitive man, perhaps as long ago as ½ to 1 million years ago.)
The first written reference to 'Irish stew' is in Byron's 'Devil's Drive' (1814): "The Devil . . . dined on . . . a rebel or so in an Irish stew.”