Who is the Muhammadan Ummah, and do current nations like Americans, English, and Russians belong to it, and who are the Ummah of Da'wah and the Ummah of Ijabah?

Allah sent Muhammad, peace be upon him, to all of humankind and jinn, and they are the ummah of da'wah (those who are called to Islam). It is obligatory for them to believe in him and in what he brought. The Prophet, peace be upon him, swore that his call was directed to the Jews, Christians, and all people, and that whoever hears of him and does not believe, their destiny is the Fire. Whoever responds to his call is from the ummah of istijabah (the Muslim nation), and this name "Muslims" is what Allah and His Messenger have approved for us.