Complex sentence: He failed because tariff preference for France violated British policy, the Foreign Office in London was unsupportive of independent diplomacy by Canada, and France was moving to new duties on foreign shipping and her embarkation and a general policy of protection.
Split into simpler sentences: He failed because tariff preference for France violated British policy. The Foreign Office in London was unsupportive of independent diplomacy by Canada, and France was moving to new duties on foreign shipping and her embarkation and a general policy of protection.