I am born and brought up in Kenya and a lot of business experience based in Kenya.
Don't be afraid to talk about expansion due to business purposes and a motivation if that is how you truly feel about it and one of the reasons why you'd like to join the firm (maybe they have a good presence there).
I would recommend using it as a supplement answer (one of the reasons why this firm over the competitor) and not the only reason due to other firms also offering the same or similar opportunities. However, if there is something specifically unique about this firm or the work they do over there then make sure you have highlighted this to show them your interest.
Also, if the firm has an office in said area/continent, your answer linked with secondment opportunities can truly showcase your interest and passion, thus showing you are keen on the firm.