One of the best way to make the economy of country stronger and stable is the promotion of its local products. Instead of importing things from other countries, under developed countries have to focus on the production and promotion of their own products. Governments should make the products of their own country easily accessible and purchasable for the citizens. This will make the economy of country stronger
It doesn't work that way
In the modern world self-sufficiency (North Korea style) is a dead end. But you really don't need to be an Einstein to understand what makes the economy strong. The real way to get strong economically is to export something nobody else can produce but which everyone wants (e.g. the American dollar)
This gives you a competitive advantage, and if you have a lot of such goods, you are the king of the hood (in this case, of the whole world). Then you can choose among the bunch of producers whose goods you need to import, if at all. Put differently, export everything that is unique and import everything that is not
It will work
If it didn't work in the past, why should it start working now?
And you can't build a self-sufficient and competitive economy even in principle. For that, you would need highly qualified workforce, advanced technology and science in every possible field, as well as the whole gamut of natural resources by far exceeding those of any competitor. No country has that in their entirety, and ironically, most of that comes through competition (read, being open). Even China, with its huge population, lacks massively in a multitude of other important areas which prevent it from building a self-contained economy that would be competitive with open economies. They will have to compete with the whole world, and the world will just beat them with the raw power
And even if purely theoretically there were such a country, it would still be economically beneficial not to close or get closed in but to trade openly with your neighbors due to multiple effects of second and higher orders (for example, logistics). The Soviets tried to pull that trick off and they still failed miserably in the end. Mate, I have nothing against self-education (which feels to be the case here) but without a good book on economics describing all these ideas in greater detail, you may easily come to very strange conclusions like the one you draw here ("economic independence is the key to a country's progress and growth"). Progress and growth come through competition, and that is impossible without being open to the outside world
