A nation's borders can be changed as a result of?
Borders can be changed as a result of war. The winner annexes
territory.
It can also be changed in peacetime, the two countries agree to
change their borders. This can be a mutually beneficial exchange of
territory.
Sometimes their is a referendum, and the inhabitants decide
either they want independence, or they want to change from one
country to another.
For example, it has just been agreed that Scotland will have a
referendom for independence in 2014. if the referendom gets a
majority, the border of the United Kingdom will change.