Who were the persians and how did they disrupt the life for the people of greece ?

Persia was a kingdom during the time of the ancient Greeks that was located inside what is now known as Iran. The Persians were expert warriors and their leaders were often covetous of lands and riches near and far, that they knew of. The Greeks clashed a number of times with them, most notable when the Spartans led by Leonidas turned back a massive invasion force at Thermopylae, and yes that was a real battle and the "Hot Gates" is a real place, as well as a number of other less well known battles. 

  it caused a pause in the usual fighting between the greeks city-states while they turned their efforts to either siding with persia, or allying against Persia, this was a great loss of life, and a loss of  of property also a disruption of agriculture.