It’s fair to say that when a lot of Silicon Valley startups think about global expansion, they’re thinking mainly of Europe and key Asian countries like Japan, China and South Korea. Yet they could be facing competition in continents like Africa if they don’t get there quickly too. Example: Motribe, a South African startup that says it has more than 1m users for two photo-sharing apps launched on the Mxit social network there: MxPix and JudgeMe. Compared to Instagram, the apps are aimed at feature phones and use the mobile web.