Complex sentence: The note was addressed and contained a death threat to Ayaan Hirsi Ali, who was subsequently forced to go into hiding, threatened Western countries and Jews and also referred to the ideologies of the Egyptian organization Takfir wal-Hijra.
Split into simpler sentences: The note was addressed to and contained a death threat to Ayaan Hirsi Ali, who went into hiding. It also threatened Western countries and Jews, and referred to ideologies of the Egyptian organization Takfir wal-Hijra.