Venezuela could lose the bulk of its oil export revenues this year if the U.S. blockade stays in place, according to internal government estimates, a scenario that would set off a humanitarian crisis.

Now that we're at a crisis point — with the United Nations saying U.S. President Donald Trump's weekend invasion of Venezuela contravened its charter and with Nicolas Maduro appearing in a U.S. court — it's a good time to review what led to this moment.