Changes in business activity
The importance of each sector in an economy changes overtime.
Industrialization is the growing importance of secondary sector manufacturing industries in developing countries
The situation is reversed in the develop countries. There is decline insecondary sector and increase in tertiary sector: De-industrialization.
Rising incomes, higher standards of living have led consumers to spend on services, eg tourism, hotels.
Due to industrialization manufacturing industries face more competition. Therefore rising imports of goods are taking market away from secondary sector