In the middle rounds of an escalating game, where armies are dispersed, is there any reason to attack isolated stacks of armies?
Example 1. Player A has an army of 6 on China. The surrounding regions, except for Siam, held by Player B, are 1's and 2's. Player C attacks and captures China.
Example 2. Player A has an army of 11 on Ontario. Player A, B, and C have various other small armies in North America. Player C holds South America and has a small stack on Central America. Player B attacks Ontario, dropping the stack to 3 men.
Do either of these moves make sense?
My general impression is that they don't. Continents aside, attacking is a zero-sum game. To kill an opponent's armies requires you to sacrifice a roughly equal amount of yours. Spending armies on taking down a large stack is a newby move, as bad for the attacker as the defender.
I understand that there are certain situations when one might want to do it anyway. For example player C thinks Player A has enough armies in China to take out Player B and sweep the board. Or perhaps Player C thinks he's got way more armies than anybody else and can afford to cripple Player A, in second place, so he can't make a kill. But, unless I'm wrong, these cases are rare.
I play a lot of open games, many of them speed games, and I come across these types of things every moves every so often.
I can only think of two explanations.
1) There's something big I'm missing. In which case, what is it? I'd love to improve my strategy.
2) These types of attacks, especially when done by more than one player in the game, are a sign of collusion, players colluding either within the game or across games.
I'm hoping for number 1! What are your thoughts....?
p.s. the examples above are hypothetical. I just tend to like stacking armies on China and Ontario.