Final answer:
For an international park to work, the two countries must have a history of peaceful cooperation.
Step-by-step explanation:
The reader can conclude that for an international park to work, the two countries must have a history of peaceful cooperation. This is evident from the statement, 'Peace held for decades, with diplomatic missions going back and forth, sharing travel, banquets and poetic toasts.' The fact that the two countries were able to maintain peace and engage in cooperative activities indicates that they have a history of working together peacefully.