Or did they always think that way? It seems difficult for me as a modern to think of the day-to-day life of someone on the coast of the Mediterranean or the Black Sea in the early modern period for example, where any day might mean a potential pirate attack by a squadron of ships traveling with the blessings of a prince or emir, as "peace".
It seems to have first happened, at least in Western Europe, during the Medieval era, more specifically during the X-XIe centuries. This idea of peace as normal and desirable sprang from a mass movement in what would later become France, led by the Catholic Church, against feudal conflicts and violence. The Peace of God was enacted in 989 at the council of Charroux and focused on protecting clerks and their lands, the Truce of God, enacted in 1027, attempted to restrict war to specific times of the year and the week (no fighting during the winter, and not from Wednesday evenings to Monday mornings).
It was an attempt to pacify the society and to establish the Church's authority over feudal lords, especially after the fall of the Carolingian dynasty: their successors (the Capetian) were then not strong enough to fight against the lords' raids and Robert II the Pious is the first king to support this popular and religious movement. It was mainly intended to protect the Church's properties and to prevent feudal conflicts from escalating, even if the population arguably benefitted from it too. The French monarchy led a strong propaganda against its English, Flemish and Imperial enemies when they lost against it at the Battle of Bouvines (27 July 1214), arguing that attacking on a Sunday was frowned upon by God and thus lost to the Kingdom of France.
It was definitely not universal, and started to fade during the XIVe century when the reason of State became a more important stake than a united, universal Christendom. Some clerks and scholars still tried to enforce it (Jean Gerson said to Charles VI of France in 1392 "Toute chrétienté est votre pays" = "all Christendom is your country", in order to deter him from fighting the English but to no avail) but it became less and less relevant as States were becoming stronger and the war effort and means intensified during the following centuries.
Peace was still held in high regard and war was obviously never upheld as an ideal but as a means. Though, war became the norm, if it could be said, as during the XVII-XVIIIth centuries Europe experienced only two years of peace, 1669 and 1770. The Napoleonic era and the rise of nationalisms during the XIXth century contributes to involve the whole population in the war effort and to establish war as a national issue in which all citizens must participate, until the early XXth century, when organizations try to promote peace (the Carnegie Endowment for International Peace, 1910), and later, after WWI, as the horrors of the Trenches War led to a mass pacifist movement in Western society.
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