The open border has helped keep the peace for 20 years. Help us make more ambitious videos by joining the Vox Video Lab. It gets you exclusive perks, like livestream Q&As with all the Vox creators, a badge that levels up over time, and video extras bringing you closer to our work! Learn more at http://bit.ly/video-lab Northern Ireland is part of the UK, but because of a special power-sharing agreement, it has an open border with Republic of Ireland. This was designed as a compromise that ended 30 years of conflict and violence in Northern Ireland between Nationalist and Unionist paramilitaries. Today, Brexit means that the UK needs to close its borders and the issue of the Irish border is one of the hardest things to negotiate with the EU. Closing this border could undermine the compromise that kept the peace for 20 years. To truly understand the international conflicts and trends shaping our world you need a big-picture view. Video journalist Sam Ellis uses maps to tell these stories and chart their effects on foreign policy. Vox.com is a news website that helps you cut through the noise and understand what's really driving the events in the headlines. Check out http://www.vox.com/. Watch our full video catalog: http://goo.gl/IZONyE Follow Vox on Facebook: http://goo.gl/U2g06o Or Twitter: http://goo.gl/XFrZ5H