Prayer and Religious Articles: Prayer and Blessings: She-hem Mishtachavim in Alenu:
Why was the sentence "She-hem mishtachavim..." deleted from the Alenu prayer?
The historians tell us that the phrase was deleted under
repeated pressure from Christian censors during the 14th
to 17th centuries. The connection (by Gematria) to
Christianity is in fact mentioned in the commentary
Arugas Ha-Bosem, written in the 1200's. For more details
see the article on "Aleinu" in the Encyclopedia Judaica,
vol. 2 cols. 555-559.
Ask a follow-up question