In chapter 13 of Leviathan, Hobbes addresses "the natural condition of mankind." He says that this natural condition is one of equality, since the differences between men are fairly trivial. While some men are stronger than others, the difference in strength is not very great so that the weakest man is able to kill the strongest, either by some kind of subterfuge or by joining together with others.
Unlike a romantic or utopian socialist, Hobbes does not think this relative equality of men is fortunate or desirable, since it includes within it the origins of conflict. Because men are approximately equal in strength, they are inclined to compete for whatever they want, since each one believes he has a reasonable chance of attaining it. This means that equality leads directly to war and that peace is not part of the natural condition of mankind.
This is what Hobbes means when he says that it is part of our natural condition for men to "live without a common power to keep them all in awe." This condition is synonymous with war. War, for Hobbes, does not consist only of actual fighting but of a precarious state of society in which fighting might break out at any time. This is why a common power is needed, to impose order on the condition of mankind and prevent it from degenerating into constant violence.