Read the passage from President Bush’s 1991 speech describing relations between the United States and the Soviet Union. Europe has become whole and free, and America’s leadership was instrumental in making it possible.

Our relationship to the Soviet Union is important, not only to us but to the world. That relationship has helped to shape these and other historic changes. . . .

. . . We will maintain our contact with the Soviet leadership to encourage continued commitment to democratization and reform.

–George Bush,
1991

What is an example of a "historic change,” as described by Bush above?

the end of the Korean War
the defeat of Nazi Germany
the Berlin airlift
the destruction of the Berlin Wall