There are now 3X as many people and they eat twice as much meat.
Agriculture needed mined fertilizer (Potash, Phosphate, etc.) since the end of the 19th Century and those sources are going to run out in a few decades.
We are emptying the oceans of fish, cutting down the remaining rainforests for beef and palm oil, and the fact we have been deliberately ignoring for as long as we have had civilization is that agricultural (and forestry) export are not sustainable.
You can't ship food to the city to support dense populations, you can't even sell it to the farmers' market forever.
Eventually the soil runs out of essential trace elements unless it is flooded every year like in ancient Egypt and Mesopotamia - OR everybody shits in the cropfields.