Why Import economies are unsafe?

In class today, I was asked why I think its dangerous for a country to base its economy on agriculture, and the processing of agricultural goods...

And import the manufactured things they need, like vehicles, farm equipment, communications equipment, power generation equipment and defensive and law enforcement equipment, from other countries.

And I said that its dangerous, because all people have a culture derived from their environment...

And its too easy for suppliers of things that needed in order to function, to malign and distort the culture of the buyer and ignore the needs of the buyer.

And even to shut down the buying nation.

And history says that.

The north did it to the south.

Europe did it to South Africa.

The USA did it to Cuba.

To be safe...

You need at least three domestic manufacturers and twenty points of sale of what your country needs, PER half a million consumers, PER area of need.