Yeah, the advent of artificial fertilizers has allowed many places, including many in the USA, to revert to monocultures.

While some farming practices have improved and remain improved, like systems for land and water retention, monoculture is only sustainable as long as the supply of artificial fertilizer - at a profitable price - remains steady. And even then, artificial fertilizers have other drawbacks - including environmental damage from overflow (especially algal blooms) and the consumption of mined phosphates - a limited resource.