How to get across, like the USA pre-1917 and 1941? (9)

I believe the answer is:

laterally

I believe this clue is a double definition.

'how to get across' is the first definition.

'like the usa pre-1917 and 1941?' is the second definition.
(the USA later became an ally)

(Other definitions for laterally that I've seen before include "Approaching the side" , "Sideways" .)

I've seen this clue in The Guardian.

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