During the period between the Second Mexican War and the Great War, tensions between the United States and Canada were high. Canada had been used as an invasion route into the US during the Second Mexican War; British troops under Charles George Gordon were repulsed in Montana territory, and a British invasion seized a portion of northern Maine. Moreover, Royal Navy ironclads were able to steam up the St. Lawrence River and shell Buffalo. After the war, the US occupation of Canada obviated the need for a fleet of (already obsolete) battleships on the Great Lakes, and the ships were scrapped.