I believe the information age is the hardest obviously because there is so much you have to do at once when attacking, like nukes, naval, air, ground, and when the future techs are complete than nukes are history, sams can't shoot down enemy bombers, cities get assimilated instantly, and well you are experts you know the rest.
The point is that it's hard, and to master defense and offense takes practice when facing tough online players or toughest computer players.
i collect resources very quickly and so im gonna cut to the chase.
if you live on an island i have something for you, and i call it the wall of fire.
redouts all around the island, fit as many as you can. than build twice as many sams next to the redouts, than build bunkers behind the redouts in case they bust through. next build your...no not navy.....air force.
the fact is that when i play online, i never win with tanks or troops, but with planes. planes can be the most destructive weapon in RON, even more than nukes. if you build seven aircraft carriers, and try and build as many bombers as you can, you can own any navy or land assault heading your way. use bombers for hit and run attacks against enemy nations, and fighters for support and eliminating tanks and navy, than use choppers for subs. PS: i never build ships, heck i don't need to. sure when you end the game, air casualties will be high, but youll win battle after battle.
after you school the enemy, you already have units in the que ready to be made, but your carriers took up all the space with their 7 fighters (if you build morew than like 12 like me). delete them and rush the enemy by SEA and take their capital. PS: the bombers are already destroying the unit production buildings, and half of your carriers took care of the fighters with air missions.
repeat the process and youll win. and if any enemies invade you, send all your citizens in, defend with air and your redouts will knock the snot off of enemy troops.
HOW CAN I LOSE THIS EASY STRATEGY? MONEY MONEY MONEY... economy is your weakness, so have a buddy for support and collect as many resources as you can.
HOW MANY CITIZENS SHOULD COLLECT RESOURCES? i say no more than 75 or 80 because you'll need military units.
WHAT IS THE MOST EXPENSIVE THING TO DO? believe it or not the most expensive thing you do is build defense and carriers (at least for me).
Last but not least... this is a gradual process that could use a good 10-15 peace time minutes to prepare for, but when completed, if you play right you'll win.