When it comes to the relation of American to British English, one of the most popular notions is that of ‘colonial lag’. As early as 1869, Ellis (1869–89: 19) remarked that American English (AmE) was more conservative than British English (BrE) in some pronunciation features:
there is a kind of arrest of development, the language of the emigrants remains for a long time at the stage in which it was at when emigration took place, and alters more slowly than the mother tongue, and in a different direction. Practically the speech of the American English is archaic with respect to that of the British English.
Others, like Bryant (1907: 281), for instance, were keen to point out that AmE was both conservative and innovative in comparison to BrE, with innovative features most obviously found in the lexicon. The concepts of colonial conservatism and innovation have been around for a long time, but the term ‘colonial lag’ was coined by Marckwardt (1958) who used it in a broader sense than the earlier notion of ‘arrest of development’. Marckwardt applied it not only to language but more generally to a whole nation and their culture:
These post-colonial survivals of earlier phases of mother-country culture, taken in conjunction with the retention of earlier linguistic features, have made what I should like to call a colonial lag. I mean to suggest by this term nothing more than that in a transplanted civilization, as ours undeniably is, certain features which it originally possessed remain static over a period of time. Transplanting usually results in time lag before the organism, be it a geranium or a brook trout, becomes adapted to its new environment. There is no reason why the same principle should not apply to a people, their language, and their culture. (1958: 80)