The American Threat The British colonies of North America felt threatened by the United States. Manifest Destiny, the belief that all of North America should belong to the United States, was a view held by many Americans during the American Civil War (1861 - 1865). Canadians were afraid the Americans would invade Canada in retaliation for Britain's actions and support of the Southern states during the course of  the Civil War.  A further threat was posed by the Fenians, Irish nationalists, who wanted independence from Britain. They had a lot of support from Irish Americans. The Fenians wanted to capture the colonies in Canada and use them to force Britain to give Ireland its freedom.

Railways
The construction of an intercolonial railway between Canada and the Maritimes was necessary since all goods were being transported on American lines and the Grand Trunk Railway needed increased traffic on its line to avoid bankruptcy. In addition, a transcontinental railway uniting the Atlantic to the Pacific would have to be built to open up the West and to prevent a possible takeover by the United States. Railway construction however was extremely expensive. The only way to ensure its construction would be for all the colonies to unite and to contribute to its construction.
 

The British Attitude
The British were interested in seeing the colonies unite, because the cost of defence could be taken over by the colonies. To the British, it made good sense for the colonies to join together to make a larger union, which would be strong enough, with some support from Britain, to stand up to the United States.
 

Try the following questions on the causes for Confederation.