The answer you are likely looking for is: Judaism, Christianity, and Islam, but this is incomplete. There are more than just three monotheistic religions in the Middle East. Other Middle Eastern monotheistic faiths include: Baha'i, Druze, Yarsan/Ahl-e-Haqq, and several other religions with a few thousand followers. Additionally, all of these titles are broad headers with many intrareligious distinctions. For example, Coptic Christians have their own Pope, while Maronite Christians are in communion with the Holy See.
Islamic Perspective on Monotheisms
Christianity used to be monotheistic, but not any longer for they now believe in 'three' rather than One
But from an Islamic point of view, Judaism is no longer monotheistic either, for they have a lot of anthropomorphism in their scriptures and they associate partners with Allah by rejecting the laws brought by His Last messenger Muhammad (Allah bless him and give him peace), which associates their own customs with His prerogative to be worshiped as He directs.
All the Christians don't believe in Trinity. Many Christians still believe in One Almighty God.
judaism
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,Islam,and Christianity
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 were all founded in southwest Asia, more specifically the Middle East.
Judaism, Christianity, and Islam.
Jerusalem
India, Judea, Saudi Arabia
Judaism, Christianity,and Islam. Judaism is the oldest of all three religions that all began in the Middle East or Southwest Asia.
Hinduism, Buddhism, and Islam
Christianity and Judaism
Judaism, Christianity, and Islam were all founded in southwest Asia, more specifically the Middle East.