Every clan could have a "night shift".
That's essentially how it was. When battles were at terrible times for EU, then friendly NA clans would merc for them, and vice versa. You had EU clans and NA clans as neighbors, and lots of times they would fight in each other's battles (even though the ping + the terrible lag of sieges [which is fixed now] would make it hard to play across the pond)
I miss strat 2's open borders, and NA and EU factions having an incentive to work with each other more (and merc in each other's battles)