World War I helped to bring about Canadian autonomy because Britain needed Canada’s help in the war. Because Canada was so important to the war effort, it was able to push Great Britain to give it more autonomy. As Canada became more autonomous, it can be said to have come of age as a real country whereas before the war it had been more like a colonial appendage of Britain.
WWI, of course, put Great Britain under extreme stress. The country needed tremendous amounts of supplies from abroad. It also needed all of the military help that it could get. Canada became an important source of both of these things. Because Canada was so important to Britain’s war effort, it was able to require Britain to give it more autonomy after the war was over. This greater level of autonomy could be seen rather immediately when, in 1922, the Canadian government refused to follow Britain’s lead in a dispute with Turkey without a debate in Canada’s own Parliament. The greater autonomy became a matter of law in 1931 with the passage of the Statute of Westminster.
A country can be said to come of age when it becomes important on an economic, political, and military level. Before WWI, Canada could not have been described in this way. Its contributions to the war allowed it to come of age and gained it much greater autonomy from Great Britain.