Explanation of Valhalla
Global Population Events:
Why I'm Doing This:
 One of the original goals - and fundamental design concepts - for SpiritWars was that it would be a game of every-changing playing challenges, constantly challenging even the most experienced and skilled player to adapt, improvise and find new strategies and styles of play.  One thing we have discovered is that over time, the playing environment can become somewhat stagnant as players accumulate large kingdoms, build up powerful spirits, and get set in their ways.

These new "population events" will introduce a new random element into the playing world; and will act as a stimulus for change, periodically making major changes in make-up and spirit configuration within Valhalla.  With each "major" event, all players will be faced with adapting to significant changes in their kingdoms and will find themselves scrambling to find new spirit combinations and dungeon definitions that will work in the altered arena of competition.
How They Will Work:
These population events will take place without any prior notice.  When the occur, it will require that I shut down the server for 5-10 minutes.  (It isn't possible to modify the spirit populations while people are playing.)  I will try to schedule these at times of low activity; and if people are online at the time, I will give them notice that the server is going to be shut down.

However, what I won't give anyone notice of is what the nature of the upcoming event is.  That you will discover after the fact.  And by examining your population and checking the Population Event History page.
Major vs. Minor:
 Major population events are just that: major.  Look at the table of event definitions and you'll quickly see which ones are major.  Removing all ranged attack pieces from everyone's kingdoms certainly qualifies as major.  As does removing all deities, or all leaders.  Major population events will not happen very often.  Don't expect to be encountering one more than every 6-8 weeks.  And, to be honest, I'm not sure yet what the ideal timing of these events will be until we all live/play through a few of them.  We need to see how long it takes the world to rebuild, populations to restore and the normal balance to be re-established.  Once I've seen that process work through a few times, I can then have a better feel for how often "major" events can be scheduled.

Minor events are of a less catastrophic nature.  Players all getting extra energy, minor adjustments in spirit counts, or forced distributions of special spirits would qualify as minor population events.  I'd like to plan on having 1 or 2 of these every month.  As with the major events, though, I don't want to commit to any fixed schedule until we've experimented.
"Serial" Events:
 Serial events are groups of major and minor events (mostly minor) that are strung together over a period of time.  These types of events will often be associated with some sort of story-line and follow a specific theme that, over time, will be revealed.  These types of events are design to dramatically shake up the playing world for a period of time.
Event History:
 The Event History page will document the date (and nature) of all Valhalla population events.  If you log on and find significant (or even minor changes) to your spirit kingdom, check this page to see if a population modification event occurred since your last visit.