While I am pretty sure that oxen-powered wagons were the primary method of overland freighting in Europe and North America, circa 1700-1815, how were goods and/or military supplies transported where roads did not exist and could not be created because of terrain?

When was freighting or packing via mules [power] introduced: to eastern North America; to Europe?

When did mules become generally available in: eastern North America; in Europe?

Don't know the answer to your questions but G. Washington was a mule breeder when he wasn't fighting revolutionary wars and running the country.

this is a good start--
http://mulemuseum.org/History_of_the_Mule.html