Complex sentence: Solf's political position was centrist; he joined the German Democratic Party ("Deutsche Demokratische Partei"), however, with its dissolution in 1933 he had planned with others to form a new moderate party.
Split into simpler sentences: Solf's political position was centrist; he joined the German Democratic Party ("Deutsche Demokratische Partei"). However, with its dissolution in 1933 he had planned with others to form a new moderate party.