Like all life, humans are completely dependent on their environment to meet their essential needs. But it is important to realize that the environment does not just impact people, people also impact the environment. This forms a feedback loop as changes brought about by people to their environment, then affect the people who depend on this environment.
Like many modern visitors to Iraq, Leonard Wooley one of the first archaeologists of Mesopotamia, was puzzled why the cradle of civilization where the first cities developed was today a desolate, barren land.
"Only to those who have seen the Mesopotamian desert will the... ancient world seem incredible, so complete is the contrast between past and present... Why if Sumer was once a vast granary has the population dwindled to nothing and the very soil lost its virtue?"
The answer to Woolley's question is that the Sumerians themselves destroyed their world. The Sumerians depended on irrigation to create the food necessary to feed their cities and maintain their civilization. However, one by-product of this irrigation was the gradual accumulation of salt in the soil as the mineral rich irrigation water would evaporate leaving the salts behind. For the same reason the ocean is salty, the fields of Mesopotamia became salty as well. Unique characteristics of the Mesopotamia exacerbated this process as the soil had low permeability, the rivers had high silt levels, and the desert climate meant nearly all water for farming had to come from irrigation. Crops (just like people) can not live on salt water, and over hundreds of years the land gradually became toxic; eventually leading to the collapse of Sumerian civilization.
The tale of Sumer damaging their environment and in turn destroying their civilization is not an isolated one. Many civilizations, such as the Mayans, are thought to have collapsed due to degrading the environment upon which they were dependent. As we impact our environment, we impact our future as well; forming a feedback loop that continues to shape the share destiny of our land and ourselves.