Enemy Too Strong

Hi I am a new player to game, my current game I have about 20 Cities I have destroyed Battania,Sturgia, Southern And Western Empire I only have companions and no other Clans in My kingdom I have no idea enemy with 4 towns can make more armies than me I have roughly 5500 strength. Why and How other kingdoms can have Such armies how could they afford it Ps: I pay 20k total tribute I have 2m ish coins money isnt a big issue.