Proposed Canon
Under conventional Erfworld tactics, the largest army a peaceful side can maintain is about half the size of a standard side, leaving peaceful sides vulnerable. The So-be-it Union's solution was to place caps on how many units each member side can pop and unite their smaller armies against enemy sides. With 4 sides in the Union, they could confront enemy armies with an army the size of 2 standard sides.
This alliance was successful for a very long time, but an enemy side named Bullyclub managed to persuade King Scrofula of Squashcourt to defect. Lord Crush of Firstpost realized that Bullyclub would only betray Squashcourt and came up with a plan to save the Union, but King Scrofula ignored it out of pride. Scrofula's son, Prince Axe Bodyspray, eventually saw the value of the plan and very literally beat sense into his father. Lord Crush's plan called for Firstpost to stay neutral at first, leaving the Union and causing it to end. The Union sides ultimately prevailed against Bullyclub, reformed with Squashcourt again being invited, and even showed mercy to Bullyclub and invited them into the Union.
 Union Terms
The So-be-it Union was a complex treaty with many clauses and terms, these included:
- Limitations for the total number of units each side can have to half a standard army.
- A minimum number of units was also set, likely to always have adequate preparedness.
- If a side defects the Union is not dissolved.
- The defection of a Union side lifts unit limitation restrictions.
- A mutual protection pact where all Union sides defend each other if attacked.
- When a member side is attacked, unit limitations are lifted.
- Diplomats from allied sides have a right under Union terms to send dispatches home via Message hat at any time.
- Union terms forbid one side from attacking another.
- (Later additions during the third war with Bullyclub) Firstpost must spend all Shmuckers gained from sacking Bullyclub's cities on units, casters and/or Barbarians to fight Bullyclub.
- Bullyclub - Shown mercy and admitted into the Union after its defeat.
It's been mentioned that magically binding contracts and alliances can be negotiated with very painful penalties, such as the one Haffaton offered to Goodminton in exchange for Wanda Firebaugh. Why neither the Union nor any of the fallen multi-side alliances Lord Crush researched had similarly crippling penalties for defecting sides is an open question. It may imply that magically binding contracts or alliances with more than two sides can't have penalties, which would make enforcing them possible only through combined shame or potential military repercussions. Though Lord Crush's assessment that Firstpost would be wiped out in fifteen turns if it broke alliance does make this a credible deterrent, it left the Union vulnerable when Squashcourt allied with Bullyclub.
 Real World References
The So-be-it Union is a pun on the Soviet Union.