Berets

Military dress is often a way of showing your cultural affiliations - and in this light I was thinking about berets the other day. When did these hats normally associated with Frenchness become the default headgear of all the world's armed forces for one thing? Apparently according to the wiki on the subject linked above they first came on the military scene with the Chasseur Alpins in the French army of the 1880s and were still largely unknown by the early 20th century. But also it was popular with tank crews as it could be worn with earphones and black was the colour that didn't show oilstains. I wonder how much the experience of the Spanish Civil War was to blame for the popularisation of the beret? The popularity of the beret can be said to be from the middle of ww2 - maybe it was symbolic of anti-fascism. Is it really a form of hatlessness that is represented in the beret as it can be shaped like human hair? Does it represent an affiliation with Frenchness in military matters? At least in a sort of casualness as a contrast to German militarism? Interesting to note the American armed forces haved resisted mostly the beret?