Final answer:
The first four provinces that joined in Confederation in 1867 were Nova Scotia, New Brunswick, Ontario, and Quebec. These provinces united to form the Dominion of Canada, initiating a self-governing entity under the British Empire.
Step-by-step explanation:
The first four provinces that joined in Confederation to form Canada in 1867 were Nova Scotia, New Brunswick, and the Province of Canada, which was subsequently divided into Ontario and Quebec. Confederation was partly necessitated by the need for a national defense system and the desire to build a transcontinental railroad. The British Parliament passed the British North American Act, thus allowing these provinces to self-govern within the framework of the British Empire, with Queen Victoria as the head of state. Sir John A. Macdonald, a key architect of Confederation and the national railway, became the first Prime Minister of Canada.