The historians of the past, from ancient Greece right up to England's Lord Macaulay liked to believe that we need to know history in order to "truly" know the modern, contemporary world. Indeed, Lord Clarendon's famous history of the English Civil War in the seventeenth century begins with the words,"So that posterity may not be deceived...!" History, said Giambatista Vico, the 17th Century Italian historian, is a cycle: what goes around, comes around.
However, I am inclined to believe that this belief has been much over rated, partly because of the ego of past historians. Modern historians and social theorists like Michel Foucault have said that real history is the history of everyday people, not to be found in the famous history books but in ordinary people's letters, diaries, newspaper stories.
Seen from such a perspective, only great wars repeat themselves, kings murder kings, usurp power, nations are attacked for love and lust, whole civilizations colonized -- all by the so-called famous men! History repeats itself because human greed, hubris, lust for sex and power are universal, existing everywhere. History does notrepeat if we observe the everyday person through eyes of not historians but scientists, sociologists, artists and novelists. They create new theories, new art and literature and are not content with looking at new life through old lenses.
Understanding the past is important for understanding the present because so many things that happen today are analogous to things that have happened in the past. If we look carefully at the past, we may be able to learn lessons about the present.
For example, the war the US fought in Iraq and the one it is fighting in Afghanistan can be seen as similar to what happened for the US in Vietnam. All were wars where the US was trying to suppress an insurgency while helping a friendly government to get going. The problems of Vietnam should have helped us to foresee the problems we have experienced in these later wars.