Previously men were dependent more on articles available in the nature. But with the advancement of human civilization; industrialization is also improving rapidly. In the recent past there was a balance between birth rate and death rate in the world. At present number of death caused by natural calamities like cyclone, famine, different fatal diseases, aggression and bite of harmful animals, is much less than as prevaile in the past. Now a day there are preventive measures for protections against the disastrous effect of every natural calamity. For example the forecast of cyclone is available before hand and taking shelter in safe places people can save their lives. With the improvement of communications system famine do not occur as frequently as before, even if it occurs food can be supplied easily.
Prevention of hunting wild animal and adopting defensive measures against their attack has made human life safer than before. Taking effective and preventive measures against severe diseases man has become able to recover from his illness and avoid inevitable death. Thus the average longevity of human being has increased. As a result with increased longevity people can give birth to children in greater number. For this increase in population the cultivable land and forest areas are gradually decreasing.
Thus the demands of agriculture as the main livelihood of our country can no longer be met from agriculture alone. For this reason it is necessary to establish industries in a well planned way. But our conventional industries are dependent on our natural resources. As the raw materials produced in our country are not sufficient for the need, thus necessary raw materials are to be imported from foreign countries.