The British North America Act, 1840 (3 & 4 Victoria, c.35), commonly known as the Act of Union 1840, was enacted in July 1840 and proclaimed February 10, 1841. It abolished the legislatures of Lower Canada and Upper Canada and established a new political entity, the Province of Canada to replace them. This act effected the political union of the Province of Canada, and was similar in nature and in goals to the other enacted by the British Parliament.
The inspiration for the act is typically attributed to Lord Durham's Report on Canada. Lord Durham was sent to the colonies to examine the causes of the Rebellions of 1837 in both Upper and Lower Canada. Lord Durham wanted to re-instate peace throughout the colonies, and recommended a political union. It was under his belief that peace could best be achieved by ensuring a loyal English majority in British North America, as well as by anglicizing French Canadians, and by granting responsible government. The union was also proposed to solve pressing financial issues in Upper Canada, which had become increasingly indebted under the previous regime dominated by the Family Compact. These debts stemmed mostly from poor investments in canals connecting Upper Canada to the port of Montreal in Lower Canada via the Great Lakes and St-Lawrence river. Due to Upper Canada's considerable debt and chronic budget shortfalls, it was hoped that its finances could be salvaged by merging it with the then-solvent Lower Canada.
Upper Canada, with its British and Protestant majority, was growing more rapidly than Lower Canada, with the French-Canadian and Catholic majority. It was hoped that by merging the two colonies, the French-Canadian cultural presence in North America would gradually disappear through assimilation. As such, the act also contained measures banning the French language from official use in the Legislative Assembly. However, despite the amalgamation, the distinct legal systems of the two colonies was retained with Upper Canada becoming referred to as Canada West (with English common law) and Lower Canada as Canada East (with French civil law). In Upper Canada, there was opposition to unionization from the Family Compact, while in Lower Canada political and religious leaders reacted against Upper Canada's anti-French measures.