The War for Halcyona
Starting at level 30 you can obtain a quest from a Golden Plains Battle Recruiter NPC, which spawn in each faction's Capital City when Halcyona goes to war, which you can turn in to your perspective factions base shortly after the war starts for 2 Warrior's Medal. This quest can be obtained and completed once every war, allowing for completion multiple times a day.
10 minutes into the war, artifacts spawn at each factions base and whomever kills the opposite factions artifact first, wins the battle and can loot 5-10 Warrior's Medals from said destroyed artifact. You do not have to participate or be present when the artifact is destroyed in order to loot it for the Warrior's Medals; however the artifact will vanish 5 minutes after its killed.