Change of allegiance
In February 2002, Cahill's former manager at Millwall F.C. Mick McCarthy, then the manager of the Republic of Ireland national team offered Cahill the opportunity to play at the 2002 FIFA World Cup. Cahill has Irish grandparents and McCarthy had hoped that Cahill would be interested.[38] However Cahill was not eligible as he was cap-tied to Samoa.
FIFA changed its eligibility rules in 2004, allowing players capped at junior levels to switch international allegiance, meaning that Cahill was then able to play England, Ireland, Australia or Samoa. He chose to represent the country of his birth.