Paradox Interactive announces a "call to arms" for strategy gamers looking forward to Europa Universalis IV asking them to help spread the word about the game "in an epic community-building campaign." This video explains the campaign (and also includes gameplay footage), and this page is where to sign up so you can collect the bonuses they are handing out to participants. Here's the deal, though they note that for some reason the trips to Stockholm have already been claimed:

The Call to Arms Rewards for loyal fans include bonus in-game DLC, a Developers Strategy Guide, Compendium Universalis, the e-books The Art of War and The Prince, and a copy of Europa Universalis III Chronicles. The “World Conqueror” rewards for the most loyal fans include exclusive beta access to Europa Universalis IV, a mention in the game credits, and a trip to Stockholm to play multiplayer with the developers.