Defense is act of protection. Defense can describe a nation's foreign policy or it can describe the actions of a lawyer against charges of their plaintiff. In sports, defense prevents the opponent from succeeding. In medieval Europe, castles were constructed by kings not only as a place of living but in the support of its population from enemies. In Physiology, defense can describe the reaction of an organism and in Psychology, it can describe an unconscious process blocking painful impulses. In Great Britain, it is spelled as defence.