You can become a US citizen automatically at birth if you:
Born in the USA
The most common way to become a U.S. citizen automatically at birth is when a child is born in the United States. Children born in the United States are not required to have an American or green card or resident parents to become US citizens at birth. The mere fact of being born in the United States automatically gives the newborn American citizenship.
Please note that there are some exceptions for children of persons with diplomatic status in the United States. A child born in the United States to a parent who is a foreign diplomatic officer accredited to the United States is not subject to the jurisdiction of United States law due to his diplomatic status. Therefore, a child cannot be considered a US citizen at birth. However, a child may be considered a permanent resident at birth and be able to obtain a green card by creating an entry.
Born overseas to American parents
Another way to become a US citizen by birth is when the child is born overseas, outside the US, but at least one of the parents is a US citizen, which meets certain physical presence requirements. For example, a child was born in Russia and one of the parents is a US citizen. There are many requirements, and in some cases, even if children born abroad do not receive US citizenship at birth, they are still eligible for the accelerated naturalization process.