No wait I change my answer - it's definitely all of the massive corporate farming enterprises both in America and worldwide.
Massive multinational farm conglomerates who bought up an overwhelmingly large portion of the world's arable land during the Green Revolution and have been using it essentially non-stop since then to churn out the record low prices and record high yields which most Americans have come to believe are both natural and their birthright.
In the process, they have been running the land into the ground - nonstop cultivation of fields depletes soil nutrients like nitrogen and phosphorus, which micro-organisms naturally accumulate. In order to maintain crop yields, nitrogen based fertilizers must be spread across them essentially non-stop. The high levels of nitrates in the soil kill the micro-organisms, preventing natural fertilization and turning the topsoil into a kind of dust, prone to being blown off in the wind. As a result, almost a third of all arable land worldwide is at risk of being turned into a man-made desert:
All across Asia Minor, the Middle East, India, and South-East Asia, land that was a breadbasket for literally centuries is on the verge of turning into drought-plagued wasteland. Places like Cyprus, once a fertile gem in the Mediterranean, are turning into sun-baked wasteland where only the hardiest weeds can grow:
But that's not all. The activation of the most massive industrial machine ever deployed quickly began growing foodstuffs in land unsuitable for farming - across the American west, where rainfall cannot support crops, aquifers were drilled to water the nitrate-rich soil. However, land that does not see large amounts of rainfall is highly saline, and as water is poured over crops it raises salt from the earth and begins to kill crops:
Like a great salt-shaker has been poured over the land, and the only cost-effective system is to pour massive amounts of water over the crops; washing away the salt, into the enormous watershed which makes up most of the American midwest:
However, that water doesn't come from no where, and principally comes from million-year old aquifers located under the earth. Many of which are on the verge of running out:
From Colorado College:
Along with being the largest aquifer in the world, researchers are now claiming the Ogallala Aquifer to be one of the fastest-disappearing. Wells that are installed to pump groundwater must be drilled at least as far as the water table to utilize the water. As they pump, the aquifer develops a cone of depression as water around the pump is drawn down. This causes wells to dry up if they pump more water than flows horizontally past it and is recharged, a process known as groundwater mining. As wells begin to run dry, farmers are forced to drill more holes further down in search of water. Groundwater in the Ogallala Aquifer is measured using a network of more than 1,200 observation wells from January to March to allow stabilization of water levels following pumping from the previous irrigation system. 
Withdrawal exceeds any replenishing rate for the Ogallala. Research indicates that the Ogallala Aquifer will dry up in 25-40 years at current usage rates.  Many areas of the High plains have been experiencing a prolonged drought-up to 5 or 6 years in a row. Many rivers have already run dry, or have come close, such the Smoky Hill River by Salina, Kansas.  The Rio Grande failed to reach the Gulf of Mexico for the first time in 50 years in 2001.  This has resulted in the increase of dependence on groundwater to sustain crops and towns. Some parts of the Ogallala have dropped 25 feet in the past 10 years. The average drop in the water table during the past 50 years is about 100 ft. In Texas, where 40% of the water comes from the Ogallala, the water table drops an average of about 2 feet every year. Where corn production is particularly intense, declines have been measured at a staggering 8 feet a year. Texas itself has removed 19% of the water from the aquifer.  Declining water levels are most severe in places where the saturated thickness of the aquifer is the least, such as northern Texas, through the Oklahoma panhandle and into western Kansas.
However, we don't just wash out salt with the rapidly diminishing water - we also wash tons of nitrogen and phosphorus into the water system. There's a 7000 mile large "dead zone" off the Louisiana coast where no marine life can live - a result of massive algae blooms creating anoxic environments as they feast on nitrogen runoff.
The same is true of Lake Erie, where the Western Half cannot support life in the summer months:
"This, finally, is the punch line of our two hundred years on the Great Plains. We&harvest wave after wave of immigrants' dreams and send the wised-up dreamers on their way; plow the top soil until it blows to the ocean; ship out the wheat, ship out the cattle; dig up the earth itself and burn it in power plants and send the power down the line; dismiss the small farmers, empty the little towns; drill the oil and natural gas and pipe it away; dry up the rivers and springs, (and) deep drill for irrigation water as the aquifer retreats." -Ian Frazier
To put it another way:
This is not the age of information.
This is not
the age of information.
Forget the news,
and the radio,
and the blurred screen.
This is the time
People are hungry,
and one good word is bread
for a thousand.
- David Whyte
Oh, and fun fact - do you ever wonderful why every picture from Iraq looks kind of like this:
Does that ever kind of bother people? Remember in school that Iraq was the "cradle of civilization", a lush fertile land believed to be the Biblical Eden? How does that square with the arid, largely desert land we see?
Oh shit it's because of exactly the same reasons as the Midwest. Irrigation of the soil for crops quickly raised salt from the ground, and raped the land of the tiny creatures that make it fertile. As a result, we have modern Iraq; the mother of civilization made barren by her children, whose broken skin we tear open and suck the black blood which is beneath.
We're all fucked, so enjoy the variety and abundance of modern food while it lasts. We made the deserts bloom, and now the petals are starting to fall off.
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