The Conquest is the important part of the game. There you can beat several NPC to unlock some Features, Heroes or Legions to proceed in game.
I can also say by my experience, how far you can beat certain maps at which level.
If something is missing, please contact me.
11/12 2012 Update: We got a new update, so some things changed. I even could reach Sandruus Crowbane with lv. 10. The conquest in lower maps are now easier to finish. Before update I saw people with lv. 14 can beat Sphinx Legion.
This is the first map. You can receive Hodur as your first servant for recruit. Pallas Athena is your first hero, who will help you for the first map.
After beating mid-bosses and bosses, they are available in your recruit panel. (not all bosses can be recruited.)
Loots: Boar Hide Harness (white armor lv. 1) and Copper Dagger (white weapon lv. 1)
After beating the boss Sphinx, you are allowed to move into 30r and to choose a faction (read -> Three Factions). Certain features will unlock during the map (read -> Basic Guide). Your first legion starts here after beating Tula Knellechoes (he's strong !!). It's open for every faction (read -> Basic Guide, if you want to know more about legions).
Loots: Voodoo Doll (white relic lv. 1), Traveller's Cloak (white cloak lv 1), Veteran's Flag (white flag lv 1), Savage Breastguard (white armor lv. 17) and Retinues's Greatsword (blue weapon lv. 13) - also from Sphinx Legion.
Now you have to decide, which map is easier to beat.
Ancestral Plain or Somua Kingdom. I would start with Somua Kingdom, because you should get fast to Aphrodite Legion for better equipments.
Be aware of Gaius the Stubborn (he's a boss, but you can't recruit him) because he's strong and made me stuck for a while...
Loots: Chiefstain's Piercer (blue weapon lv. 25), Refined Chestpiece (blue armor lv. 21), Ornamented Javelin (green weapon lv. 21) and from the Aphrodite Legion Lion-Hearted Breastplate (green armor lv. 25).
After beating Raphael, you can migrate to the next region (40r).
Loots: Berserker's Blade (blue armor lv. 17), Chiefstain's Piercer (blue weapon lv. 25) and from Raphael Legion Refined Chestpiece (blue armor lv. 21)
Loots: Bite of Sabertooth (blue weapon lv. 29), Dark Iron Tunic (blue armor lv. 29) and from Crassus Legion Lion-Hearted Breastplate (green armor lv. 25)
After defeating Heine, you can migrate to the next region (60r).
Hannibal (Unit: Combustion Chariots)
Heine (Unit: Bard)
Loots: Dignified Flail (blue weapon lv. 33), Cyclone Sunderer (green weapon lv.33), Lion-Hearted Breastplate (green armor lv. 25), Judgement of Justice (yellow weapon lv. 25) and from (Heine) Attilla Legion (somehow the boss is still Heine) Mithril Breastplate (green armor lv. 29)
Here again you can choose between two paths. Furyshaw will continue your journey while Melody Garisson will be another end of the map.
Until now you could beat the maps at level 30-40.
Loots: Nightmare Greatsword (blue weapon lv.37), Demon Slasher (yellow weapon lv. 37), Steel Hand Blade (green weapon lv. 37), Mithril Breasplate (green armor lv. 29) and also the Leuce Legion gives you Demon Slasher
Many people would farm St. Simon Legion for the precious red weapon.
Loots: Compassion of Holy Light (blue weapon lv. 41), Chestguard of Dark Night (green lv. 33), Ponceau Dragoncover (yellow armor lv. 45) and from St. Simon Legion Saber of Luminosity (red weapon lv. 45)
To know more about the higher maps, just tap continue.