The Great Coalition was a grand coalition of political parties, that brought the two Canadas together (Canada East and Canada West) in 1864. The previous collapse after only three months of a coalition government formed by George-Étienne Cartier and Conservative John A. Macdonald and liberal George Brown, (the sixth government in six years) had demonstrated that continued governance of Canada East and Canada West under the 1840 Act of Union had become untenable. In order to reform the political system, a coalition was formed between the Clear Grits under George Brown, the Parti bleu under George-Étienne Cartier, and the Liberal-Conservatives under John A. Macdonald. The formation of this coalition on June 22, 1864 under George-Étienne Cartier and John A. Macdonald, as the colonies of the Canadas led directly to Canadian Confederation in 1867. The coalition persisted as the government of the Province of Canada until the moment of Confederation.
The Great Coalition was created to eradicate the political deadlock between Canada West and Canada East. The government at that time was unable to pass any legislation because of the need for a double majority. In order for a bill to pass in the Legislative Assembly, there had to be a vote in both Canada East and Canada West sections of the assembly. As the French and the English could never agree on anything, this caused political deadlock.
The deadlock lead to the three conferences that lead to confederation. The Charlottetown Conference, where the politicians were supposed to discuss the idea of a Maritime union. They chose to talk about the colony of Canada, and took the opportunity to discuss the possibility of a larger union that would include all of British North America. The Quebec Conference was to further discuss the union of British North America and to define the details of what shape that government would take. They settled on Provincial and Federal responsibilities. The London Conference was to get rid of and refine The Quebec Resolutions.