Simplify the following text for a Grade 9 native English-speaking person.
Original: Thereafter , with the US focus shifting to Iraq , Tony Blair decided to support the United States in the 2003 invasion of Iraq , despite huge anti-war marches held in London and Glasgow .
Simplified: Despite huge anti-war marches being held in London and Glasgow , Tony Blair gave strong support to the United State 's invasion of Iraq in 2003 .