Adding quest to get random resource will be fun. You can make the answer/key scattered all around the map, and players must explore to find them. 

The grey area is boring to look at. Why dont you add sand texture to fill it?

When we die, sometime we would like to just watch others player. 

At some point after playing for a while, I start being chased by groups of 4 or 5 barbarians. There is nothing I can do except fight them. This starts getting quite annoying especially if I have low health; I can't even get far enough away to heal myself before they're on top of me.

I understand this might be part of a balancing mechanic where the most powerful tribes have to deal with these barbarians. So if we can't get rid of the chasing barbs, maybe you could:

1. Slow down the chasing barbarians, making it easier for one to heal their tribe or put an enemy tribe between yourself and the barbs
2. Limit the time or distance over which they will chase you
3. Increase the barbarian respawn time so that at least the barbarian threat can be reduced after several large battles.

I might be really dumb, but how do you team up with other players? Is it based on color? I don't think I have ever seen a allied tribe...

To make battles more interesting, there could be stances for you army. For example, you could have a defencive stance where your minions would take less damage but wouldn't move, and a charge stance where your minions will charge toward your totem, doing more damage and moving fast, but turning much slower. Also it would be nice if, when you do into a stance, your minions will aline in a way that is best for combat, (melee minions in the front, archers in the back). I also think it would be good if minions took more damage if they are hit from behind or the side, so then flanking could be usfull. It might be kinda hard on mobile tho... 

please men you are good of I.O games.

Single player/tutorial mode

I always hit the max level and I can't choose between the Legion Helmets or the Steel Shields! I think the Legion Helmet is better, but I'm not so sure.