If we look at real prices for the last 50 years we get a different result, In  1972, Nixon signed a 3 year deal with the soviets to buy grain, they bought what amounted to a sizable amount of ending stocks for wheat, which, had unforeseen consequences for not  only food prices here in the US but around the world,
  Nixon and Kissinger wanted to gain leverage over the Soviets by using grain as one of the bargaining chips. I would call that "power politics". 

 The USA today is using "power politics", by using soybeans as a bargaining chip.