The Gambia needs a map to explain:

Useful BBC Profile:http://www.bbc.co.uk/news/world-africa-13376517 and their latest comment is:http://www.bbc.co.uk/news/world-africa-38650266

Mr Jammeh recently lost an election to Mr Barrow, which he hotly contested and IRRC was appealing to the Supreme Court (which in the BBC link is explained, a very odd court). He has been a dictator for a sometime now, which led to not inconsiderable numbers seeking a better life in Europe via illegal migration routes.

ECOWAS and the AU have condemned his decision, so ECOWAS issued an ultimatum for Jammeh to stand down and Senegal (which surrounds Gambia) stated it would intervene.

Two days ago as conflict loomed the UK Foreign Office issued a travel advisory, so one UK tour operator evacuated 1k tourists:

On BBC Radio Four there was a locally based reporter who added some context: there were 3k tourists normally, mainly Anglo-Dutch and 5k "sunbirds" who were year-round residents. In the past IIRC sex tourism was a big factor, for mainly older women from Scandinavia. Perhaps they make up part of the "sunbirds"?

Via this article:https://theconversation.com/high-stakes-as-west-africa-prepares-military-action-against-gambias-jammeh-71481?

I found this background briefing:http://www.everyculture.com/Cr-Ga/Gambia.html