The two changes that boundaries experience on a regular basis are due to peaceful agreements and wars.
Peaceful agreements: On March 30 1867, the United States reached an agreement to buy Alaska to Russia for a price of 7.2 million dollars.
The handover of Hong Kong from England to China on July first 1997.
When the Soviet Union crumbled many republics gained independence. It ocurred oficially on December 26 1991
Wars: After the Mexican-American war (1846-1848), Mexico lost more than the half of its territory.
After the first and second wars there were many chanches of boundaries and territories.