Complex sentence: Dutch athletes have competed in every Summer Olympic games since their official debut in 1908 with the exception of the 1956 Summer Olympics in Melbourne, which the Netherlands boycotted because of the Soviet invasion of Hungary.
Split into simpler sentences: Dutch athletes have competed in every Summer Olympic games since their official debut in 1908. Netherlands, however, boycotted the 1956 Summer Olympics in Melbourne, because of the Soviet invasion of Hungary.