The Statute of Westminster
For many years, Canada had been leaning towards becoming a nation entirely independent of Britain. In WWI, the Canadian Corps were created separate of the British Corps, one of the early steps towards autonomy. At the end of the war, Canadian Prime Minister Borden fought hard for a separate seat for Canada at the Paris Peace Conference and for a separate signature on the Treaty of Versailles, both of which he was granted. The Halibut Treaty was the first time when Canada refused Britain's request to ratify the document. During the King/Byng Crisis, Canada's citizens chose to blame the British-appointed Governor-General for using his authoritative power, showing a strong movement towards political independence.
All of the above events pressed for greater national autonomy, and each capitalized on the successes of the previous event. In 1931, all of the work carried out by the former prime ministers and governments was rewarded with the creation of the Statute of Westminster.
Creation of the Statute
The last Imperial Act carried out by the Parliament of Great Britian which applied to all of its Dominions, the Statute of Westminster gave Canada, Newfoundland, South Africa, New Zealand, Australia, and the Irish Free State the equivalence of independence. The Statute formally recognized the Balfour Report under British Law, and stated that all Dominions were equal in stature to Great Britain and each other. Canada became officially autonomous, and independent of its colonial powers. The British Empire ceased to exist, and became the British Commonwealth of Nations.