The purpose of the Dewdney Trail was to prevent draining the Interior's gold and other resources to the United States, as well as to be able to deploy troops should trouble break out and either Indian war or outright annexationist uprising should arise in areas where access to and through the United States was far easier than from the Coast.
The main goal of the Dewdney Trail was to safeguard Canada's natural resources, particularly gold, by preventing them from being exploited by the United States. Additionally, it aimed to facilitate military deployment in case of an emergency or uprising in areas more easily accessible from the U.S. than from the coast.