. . . Belgium .
Germany had invaded Belgium and was aiming to France. He took many ships into the Belgium ports so Britain declared to be threatened by the German ships in the Belgium ports. So Great Britain entered the war with France (something which Germany didn't expect).
Yes Great Britain was an ally to France and Belgium.
Britain is an island and Belgium is on the European mainland.
Great Britain entered WWI because of the idea of collective security, where an attack on one country means an attack on all other countries in the alliance. Therefore, when Germany invaded Belgium, G.B declared war on Germany.
Great Britain was because the British had pledged to defend Belgium.
Poland
Great Britain entered WW2 because of an alliance treaty with Poland.
Great Britain, Belgium, Italy, Russia, Siberia, Albania, and Montenegro
Belgium was the cause of friction between Great Britain and Germany in WW1. Belgium and Great Britain were allied, so when Germany invaded Belgium, Great Britain was obligated to side with Belgium and declare war.
Britain
Great britian