Have there been other instances before or parallel to Christianity where war, revenge and conflict was repudiated or not seen as an ideal - and instead peace and love for the others (love for the neighbor) was one of the core ideals?
Buddhism predates Christianity and some believe some of the ideas of Buddhism traveled along the Silk Road and reached the Middle East. They may have influenced thought in that area in the years before the appearance of Christianity.
Buddhism, although some would argue it’s not a religion, does promote peaceful co-existence. The five precepts are:
To refrain from taking life (non-violence towards sentient life forms), or ahimsā;
To refrain from taking that which is not given (not committing theft);
To refrain from sensual (including sexual) misconduct;
To refrain from lying (speaking truth always);
To refrain from intoxicants which lead to loss of mindfulness (specifically, drugs and alcohol).
Wikipedia has an article on Buddhist influences on Christianity.
Without going into details, however, I believe there are arguments against the perception of Christianity as entirely peaceful and repudiating things like revenge (eternal punishment in Hell for starters).