The First World War caused a number of changes in the economic, social and political development of Canada, which required the North American Dominion to reflect on the need to transform its channels of diplomatic communication with the British Government. The article deals with the system of intrapersonal communication based on the example of the oldest British Dominion — Canada, and its evolution under the influence of internal and foreign political circumstances connected with the global world conflict. The appeal to the analysis of the Canadian-British military interaction during the First World War as part of Canada's foreign policy is conditioned both by the need to consider the specifics of this interaction and its importance for the formation of the former British dominion as an independent actor in international relations. During this period, the foreign policy dialogue between Canada and Great Britain acquires greater stability and dynamism, and if at the beginning of the War it represented a typical example of the mechanism of communication between the dominion and the metropolis, by the end of 1918 some features of the diplomatic communication of two independent states could already be distinguished in them. Changes within the Empire become obvious and irreversible, although at this time interval the principle of «diplomatic unity of the Empire» was still decisive for the entire system of intrapersonal relations.