Complex sentence: In 1626, he was named ambassador to England and in 1629 he moved on to become ambassador to France where he succeeded in persuading King Louis XIII to enter into an alliance with Venice in order to prevent troops of the Austrian Habsburgs from occupying the Valtellina.
Split into simpler sentences: In 1626, he was named ambassador to England, and in 1629 he moved on to become ambassador to France. During his time as Venetian ambassador to France, Contarini persuaded King Louis XIII to enter into an alliance with Venice in order to prevent troops of the Austrian Habsburgs from occupying the Valtellina.