Simplify the following text for a Grade 19 native English-speaking person.
Original: In July 2008 he announced his intention to run again for the office of Mayor of London at the next mayoral elections and signalled his intent to organise a `` progressive alliance '' of political parties ( such as the Labor Party and the Green Party of England and Wales ) , trade unions and interest groups to defend the progress which was made during his terms as Mayor and to prepare for the next mayoral elections .
Simplified: In July 2008 he announced his intention to run again for the office of Mayor of London at the next mayoral elections and signalled his intent to organise a `` progressive alliance '' of political parties ( such as the Labor Party and the Green Party ) , trade unions and interest groups to defend the progress which was made during his terms as Mayor and to prepare for the next mayoral elections .