If practical, I suggest the base capture limit per country be 25%. As an example, the Rooks took 30% of the bish bases last night. That would be limited to 25%.
When two countries join to attack one country, you can drive players out of the game. Nothing worse to sign on AH and find you have limited battle fronts. This is especially true if you have to fly in troops.
Not a huge problem but a 25% limit might help when two countries attack one country.