On Wednesday, British Prime Minister Theresa May began Britain's exit from the European Union by invoking Article 50 of the Lisbon Treaty.
It started a two-year process of departure — and for now, we know little about what that will look like. When its members signed the Treaty in December 2007, no one could imagine circumstances in which a nation would leave.
On one extreme, Britain could crash out of the EU without any deals on trade, migration or other substantive issues. Or it could agree to a "hard Brexit," regaining the right to limit EU migration within its borders, but losing access to the single market.