There are about 120 million US citizens
50
Whatever the quota is that year.
The citizenship in the US in 1919 during World War 1 was approximately 104 million people. At the beginning of World War 2 in 1939, the population was just over 130 million.
No
many
Because it is the citizenship of one of the most economically advanced countries in the world. Plus, the US is the world's super power; therefore, you can't worry about sanctions when you live there.
They are US Citizens.
Citizenship now includes more types of people.
You can apply for dual citizenship to the USA and almost any other country. Many more people than you might think hold dual citizenship. But the road to dual citizenship, with only a few exceptions, is long, twisting and full of "gotchas".
If you apply for citizenship in another country your US citizenship is automatically revoked. The US does not recognize dual citizenship. You revoke it in writing at a US embassy, outside the US.
Russian law says no to it, but I know a lot of people does have Russian and USA citizenship!
People who come to the US from foreign countries go through the naturalization process in the US for the achievement of citizenship and nationality in the US. Once you become a US citizen you qualify for many government benefits.