Why is the united states so well guarded from invasion?

Aprovision of the general agreement on tariffs and trade treaty (gatt)increased taxes on services between the us, mexico, and canada.reduced international tariffs on industrial goods by forty percent.increased us tariffs on agricultural products by forty percent.ended taxes on goods traded by the us, mexico, and canada.

What are the basic input of iron and steel industry

Prices for products became more affordable as a result of new forms of ,witch got things to market faster and cheaper