Answer:
A. The US buying Alaska from Russia in 1867
Step-by-step explanation:
The purchase of Alaska from Russia changed the political maps of the United States because the new territory was added to the country. In other words, the governmental boundaries of the United States expanded since Alaska was not anymore a part of Russia or under its government. With this purchase, the US added a new state that cartographers show in a US political map in a corner along with Hawaii. In bigger political maps, where other countries are also present, it is in the same color as the rest of the US. As it is not close to the other states, Alaska is represented this way.
All the other options do not change the borders of a political map because those events do not affect the governmental boundaries that a country has