The future of Northern Ireland -- part of the United Kingdom -- has become a major obstacle to a Brexit agreement. The British government has said that as part of Brexit it wants to leave the EU single market, the area in which goods, services, capital and people move freely in Europe. This would allow the United Kingdom to honor several Brexit promises, such as gaining full control of its immigration policy. But it also creates a problem with Northern Ireland: Some kind of border control with the Republic of Ireland would have to be introduced to oversee goods moving across the common border, but border controls are prohibited under the Good Friday Agreement -- a peace deal which ended years of conflict in Ireland....
