Please explain the structuralist theory of development.

The structuralist theory of development argues that the
governments of developing countries must intervene to ensure that their economies will
be able to become fully modernized and industrial.  If governments do not do this, they
will be doomed to remain in a colonial relationship with the rich
world.

This theory was mainly applied to Latin America.  It
argued that Latin American countries would be used by the US as sources for raw
materials and cheap labor unless their governments took steps to prevent that. 
Structuralist theory argued that governments had to protect "infant industries" in their
countries from foreign competition.  The most usual was to do this was through tariffs
that would be placed on imports.  By increasing the cost of imported goods, the
government would allow new domestic industries to develop until they would be able to
compete on their own with industries from the rich world.