Nothing.
If by "the religions of Southwest Asia" you are referring exclusively to the three monotheisms (Judaism, Christianity, and Islam), then the unifying trait is monotheism.
However, there are numerous religions from Southwest Asia such as Zoroastrianism and Mandaeism whose adherents are henotheists or polytheists.
judaism
Judaism, Christianity, and Islam were all founded in southwest Asia, more specifically the Middle East.
Islam,Christianity,and Judaism
Southwest Asia in general, they were in different parts of it but close enough together to be "The Birthplace of Three Religions"
Judaism, Christianity,and Islam. Judaism is the oldest of all three religions that all began in the Middle East or Southwest Asia.
judaism
Christianity and Judaism
Hinduism, Buddhism, and Islam
Judaism, Christianity, and Islam were all founded in southwest Asia, more specifically the Middle East.
Judaism, Christianity, and Islam were all founded in southwest Asia, more specifically the Middle East.
Islam,Christianity,and Judaism
Judaism, Christianity, and Islam.
some religions include Islam, Hinduism, Catholicity, and Christianity depending on the country
Southwest Asia in general, they were in different parts of it but close enough together to be "The Birthplace of Three Religions"
Jerusalem
Judaism, Christianity,and Islam. Judaism is the oldest of all three religions that all began in the Middle East or Southwest Asia.
India, Judea, Saudi Arabia