What makes one a part of the Ummah?

According to the accepted answer in the linked question below, an ummah is " the whole community of Muslims bound together by ties of religion". But didn't earlier Prophets have their own ummah? Is it not said that ours is the last of all ummah? Are Jews not from the Ummah from Moses and Christians from Jesus? I guess what I'm trying to ask is if an individual belongs to the time/era/geography of a Prophet but does not ascribed to the message, is he/she still a part of that Ummah? Are present day *Jews/Christians/Hindus/Sikhs/Buddhists/Zoroastrians* part of Muhammed's Ummah or are they part of their Prophet's Ummah but now have gone astray from the straight path? **Linked Question :** What does “Ummah” mean in Islam?