[1][2] Owing to his dissatisfaction with the conduct of the Conservative ministry during the Red River Rebellion in 1869-70, he abandoned that party, and in 1872 unsuccessfully contested Algoma in the Liberal interest.

[1][2] Denison was one of the founders of the Canada First movement, which did much to shape the national aspirations from 1870 to 1878, and was a consistent supporter of imperial federation and of preferential trade between Great Britain and her colonies.

The best known of his military works is his History of Modern Cavalry (London, 1877), which was awarded the Czar of Russia Prize in an open competition in 1879, and has been translated into German, Russian and Japanese.

[1][2] He was a public defender of Upper Canada College, and was also known for virulent Anti-Americanism; after a proposal was made to erect a statue of George Washington in Westminster Abbey, he threatened that if it were built, he would go there to spit on it.

[4] As Norman Knowles argues in the Dictionary of Canadian Biography, Denison’s "identification with the South came naturally: it represented an idyllic society that embodied the social order, conservative values, and chivalric traditions he wished to see maintained in British North America.