The Maritimes are three of the easternmost Canadian provinces, being New Brunswick, Nova Scotia and Prince Edward Island. This term does not include Newfoundland and Labrador, which is defined with the Maritimes as Atlantic Canada due to its proximity to the Atlantic Ocean.
In the lead-up to the creation of the Dominion of Canada, the creation of a Dominion of the Maritimes was mooted, before The Canadas (Upper Canada and Lower Canada, aka, The Province of Canada) joined the confederation convention.
The Maritimes in "Elder Skelter"
The Maritimes had split off from Canada when the country Balkanized. An international crisis arose when the Republic of Quebec invaded the Maritimes. The Maritimes issued a call for arbitration and peace-keepers from the United States.
The Maritimes in Southern Victory
Parts of the Maritimes, including New Brunswick and a portion of Nova Scotia, were quickly occupied by the United States early in the Great War. The rest were surrendered in 1917. In the process, a part of New Brunswick was returned to Maine, whence it had been conquered during the Second Mexican War.