Tariffs and subsidies distort commodity prices, and commodities are global assets. In a totally free market, goods would flow around the world from the lowest priced producers to the consumers willing to pay the most. That efficient economic model is great in theory, but in practice, government policies around the globe often get in the way of economics.
The demand side of the fundamental equation in commodities is sensitive to price levels. However, the ever-growing population on our planet, combined with increasing wealth in formerly emerging markets is a dynamic that points to increasing requirements