In World War II, Working people from America, still reeling from the economic disaster (caused by reckless and nefarious bankers) known as the Great Depression, joined with British citizens under Winston Churchill, who used the hand-signal "V for Victory" to rally brave souls to protect their homes and families from the concentrated power of economic royalists (known as fascism), which was rampaging across the civilized world, motivated by anger, resentment and fear: the embodiment of greed-fueled hatred. 

A generation after that war, the children of the brave people who stopped that totalitarian/fascist onslaught began to recognize its resurgence in their own governments, in the form of an escalating arms-race amid aggressive, oppressive, thinly-veiled imperialism.  They adopted a circle with the semaphore symbals for "N" and "D" (standing for "nuclear disarmament), along with Churchill's "V for Victory" hand signal; and their overall call to the world was for Peace.  Thus the circle and hand symbols became known as references to peace in addition to their origional connotations.  Throughout this, the struggle has been one of organized human beings (generally in unions) against mindless capital that values profit above all else.  This struggle is thus a struggle for the survival of humankind.