As if the farmland would just go away, if the subsidies would go away?

> The staple native grain of Europe is wheat, rice in Asia, and corn in the Americas.

Not sure what you mean by native? The predecessor of wheat was native to some parts of the Middle East, but until recently you couldn't even grow that stuff well in eg most parts of Germany. (Hence Germany's enduring love affair with rye bread.)

Rice only grows in some parts of Asia. (Eg Northern China relies on other grains.)

All those crops are human interventions in their wide spread, they aren't native to entire continents.