I am of the opinion that the great kilt was brought about by three separate factors. The first being the more wide spread use of firearms in the Highlands; the second being the heavy export of both flax and finished linen from Scotland; the third being a general increase in poverty throughout the Highlands, at this time

Prior to the appearance of the great kilt, the typical dress of the Highlander would have been coarse linen trousers reaching to somewhere between the knee and ankle; leather shoes similar to the moccasins of the American Indians, and a linen shirt reaching to mid-thigh, or perhaps as far as the knee. Over this, in time of war, would have been worn the Leine Croich-- a knee length jacket, padded and pleated as a sort of "soft armour". The Highland soldier would have also worn a chain mail coif over his head and shoulders, and a padded leather "arming cap" under a pointed conical iron helmet. A plaid would also have been worn (or carried) to serve as a cloak or blanket as the case may be. Add to this a short spear or pike, a sword, as well as a shield, and your typical Highland warrior was as well protected as could be expected. Until the appearance of firearms. The Liene Croich was probably the first item to fall by the wayside as a result of this technological advance in waging war.

As the Highlands (and, indeed, all of Scotland) continued to slowly sink into a vast and inescapable pit of economic depression, the export of linen dried up local supplies, with the result that by 1686 a pair of ordinary linen breeches were worth 4 pounds-- more money than many Highlanders would see in a year. Bereft of liene croich, and unable to afford linen trousers, the Highlander simply wrapped his plaid around his waist and made do as best he could.

It is my opinion that it was the increase in the use of "gonnes" coinciding with the lack of the availability of inexpensive linen, that caused the almost "overnight" appearance of the kilt. In other parts of Europe-- and this includes Ireland-- where people lived in mountainous regions, tended flocks, were out in all weathers, the kilt did not evolve, and trousers remained the mainstay of masculine attire.