Does one country need all industries?

Tactically, I don't think one country needs all industries; however, in reality, this is not practical. If one industry is important but has significantly low productivity,  one country has to obtain it in its economy otherwise it could become dependent on other countries' imports. All countries want independence, economic as well as political independence. Within an economic and political union, it is reasonable for each country in the union to focus on their most productive industries and trade with each other. This could improve the productivity of the union and decrease the cost of production.