Brexit refers to the departure of the United Kingdom from the European Union. The EU is an economic and political union of 28 European countries established after World War II. A referendum was held in 2016 on whether the UK should remain in or leave the EU, with 51.9% voting to leave. Supporters of leaving argued it would restore UK sovereignty and control over immigration, while supporters of remaining argued it would cause economic uncertainty and job losses as companies relocated. After failed attempts to negotiate a withdrawal deal, Prime Minister Theresa May resigned and was replaced by Boris Johnson, who also failed to finalize a deal by the Brexit deadline of October 31, 2019.