Being a headgear enthusiast and a history buff has opened a whole world of different headcoverings and the hows and whys of their being. I'll be most likely covering hats that have a scottish connection, though some countries' hats are too fascinating to leave be. That said, I believe I'll start with scots/french influences.
It seems as though the scots/french connection can be traced back to at least the iron age when celts, the broadest term currently used to define the various disparate cultures within, populated all of the british isles, most of the iberian (spanish/portuguese) peninsula and the westernmost parts of europe (Belgium, Amsterdam and western France). Apparently it is the blood to accept a certain amount of interplay between the national fashion sense.
Nearly everyone today can make a connection between the scots Balmoral/Bonnet and the french Beret. Not nearly so well known is an obvious (at least to me) connection between the french shako and the scots kilmarnock.
Ian....I think you've out-hipstered yourself. That being said this is awfully fascinating. Question, if we're on the subject, just out of curiosity, what is the origin of the shako and the kilmarnock?
Given that the term "Celt" seems to be an umbrella term that includes a rather vast number of tribes and clans that share a distant ancestry, I think a shared fashion sense may be a bit beyond that connection. I think it may have more to do with function. These hats can all be traced back to a style that dates to the bronze age. It, like the helmet known as the "war hat" has an almost unbroken line of variations that take it into the modern day and almost all over the world. It is true that France and Scotland have historically been allies, but he head gear (in its own regional variations) seems to predate any formal alliances. But, I'm no expert.