The word "Acadia" – "l'Acadie" in French – is a corruption of "Arcadia," that region of Greece which represented pastoral tranquility. The region was so-named because of the temperate climate and the rolling green landscape of Nova Scotia, New Brunswick, Prince Edward Island (which the French called "l'Île-Saint-Jean"), northern Maine, and the Peninsule Gaspé.
The French settlers lived mainly agrarian lives, but there were several fortresses of tactical significance built in the region as well, including Louisbourg on the north-eastern coast of what is now called Cape Breton Island. Les Acadiens, as the settlers were known, also had some peaceful relations with the other significant military force in the region, the Mi'cmagh.
In the early 18th Century, war broke out between England and France; France, having lost that war, relinquished control over its two northernmost New World colonies — l'Acadie and Nouvelle France, which the British would call "Lower Canada" and later still as Québec — as part of the terms of peace. France retained control of Louisiana and the inner southern mainland. This acquisition effectively extended British control to cover the entire eastern seaboard of the New World as far south as Florida (which was still controlled by Spain).
Les Acadiens were peaceful, and because most of them thought of themselves as Acadians first and French second (if at all), they really couldn't care less who owned their territory, so long as they were left alone. The British, however, considered the alligiance of the Acadians to be too much of an unknown variable, and decided that it would be a good idea to make them pledge allegiance to the King and convert from Catholicism to one of the religions then permitted under British law. Some Acadians converted so that they would not be deported.
Most Acadians, however, thought this was incredibly stupid, and refused to convert or pledge allegiance to their new monarch. They were therefore forcibly deported, relocated en masse to Louisiana. In the mouths of the British soldiers, "Acadiens" became "Acadians" and eventually "Cajuns", as their descendents are still known in Louisiana today.
I used to work as a telephone surveyor. One day, we were calling Louisiana. One woman noticed that my accent was significantly different from her own Southern Drawl, and she asked me where I was from. When I told her that I was from Prince Edward Island, she said, "Oh, my ancestors came from that area. Say, are you Catholic or Protestant?"
I replied, "Well, ma'm, my ancestors were the British; they were Presbyterian."
She then told me a story about a 280-year hate-on that had been continuing between her own family and her cousins in Nova Scotia; it seems that many Louisianans still consider French Maritimers to be sellouts.