An Irish cross-border trade involves a lot of agricultural produce, trade in Northern Ireland would face higher tariffs compared to estimates for the UK as a whole. Although a substantial fraction of products would face no tariff, the small percentage of products that would incur tariffs of over 35% make up a significant share of cross border trade. The natural co-operation and trade across the Irish border reflects its context: it is a rural, under-developed, close-knit region. There are complex supply chains in agri-food and myriad micro-traders. WTO rules will not preserve this situation but introduce a significant level of friction in a place where border controls represent a potentially dangerous step backwards in politics as well as economics. I fully expect a barrage of abuse from Brexiteers, but there you have it. Brexit, troops, Northern Ireland- how has it come to this?