Complex sentence: While service wings continue to be built for hotels etc in domestic use they have declined along with the numbers of staff kept, this decline began in Europe following World War I. In Europe many owners of large mansions have gone as far a demolishing whole service wings.
Split into simpler sentences: While service wings continue to be built for hotels and similar buildings in domestic use, they have declined along with the numbers of staff kept. This decline began in Europe following World War I. In Europe many owners of large mansions have gone so far as to demolish whole service wings.