British policy shifts in the 1840s–1860s made Confederation (1867) both necessary and possible for the British North American colonies:
Britain repealed Corn Laws (1846) and Navigation Acts (1849), ending colonial preference. Colonies lost guaranteed markets → sought larger internal market via union.
Britain accepted colonial self-government (executive responsible to elected assembly). Colonies gained control of domestic policy—including the power to unite.
U.S. Civil War (1861–65) showed both the danger of disunion and the threat of American expansionism (Manifest Destiny, Fenian raids). Britain hinted it wouldn't defend colonies indefinitely.
Britain encouraged (and capital markets financed) a transcontinental railway—only viable as a national project. Confederation provided the political framework.
Canada West (Ontario) and Canada East (Quebec) had equal seats but divergent interests → legislative paralysis. Confederation offered federalism: shared national powers + provincial autonomy.
Colonial Office saw Confederation as a way to consolidate administration and cut defense costs—a self-governing dominion could defend itself.
Result: British North America Act (1867) created the Dominion of Canada—British in origin, but driven by colonial agency and British strategic retreat.