Complex sentence: The club was founded on 9 June 1905 when a number of youth clubs in south-east London, including East Street Mission and Blundell Mission, combined to form Charlton Athletic.
Split into simpler sentences: The club was founded on 9 June 1905. This was when a number of youth clubs in the south east London area, including East Street Mission and Blundell Mission combined to form Charlton Athletic.