Complex sentence: Immediately after the September 11 attacks U.S. officials speculated on possible involvement by Saddam Hussein; although unfounded, the association contributed to public acceptance for the 2003 invasion of Iraq.
Split into simpler sentences: Immediately after the September 11 attacks U.S. officials speculated on possible involvement by Saddam Hussein. Although unfounded, the association contributed to public support for the 2003 invasion of Iraq.