Because its the largest city in its country or its region
The U.S. wanted to prevent the spread of communism.
Differences between the Troposphere and the Stratosphere:
The troposphere is the lowest level of the atmosphere, so it is in contact with the Earth’s surface. In contrast, the stratosphere is located above the troposphere, so it is not in contact with the Earth’s surface. Humans live in the troposphere, not the stratosphere. People only spend time in the stratosphere is when they are traveling through it on an airplane, or flying through it while riding in a rocket. The air density and air pressure are much lower in the stratosphere. In fact, stratospheric air is too thin for people to be able to survive without pressurized air to breathe.
