[Baalz]

Well, assuming you're playing to win you always want to avoid a fair fight. If you attack the leader early on...even if you win you'll be weakened enough that the guy who gobbled up a couple smaller guys while your war dragged on will gobble you up. Later on in the game though things do tend to shift once its more likely that people gang up on the leader...thus still avoiding a fair fight. The main problem is that people are so abysmal at accurately assessing other player's power level so the guy with the most provinces gets dogpiled by the guy with the most research and the guy with the surging blood economy while the guy who put up Forge of the Ancients sits alone in the corner.