I've just started in my first game and am confused as to why I have only been able to deploy 13 armies so far.

Any attempt to deploy more by clicking on the barracks(I have 25 spearmen and 21 swordsmen ready) is greeted with the message "Sorry, you cannot create more than 20 armies at this time."

But I only have 13 armies on the board, so what gives? Am I missing something vital here?

Am building a military academy but its still under construction, but even so shouldn't I be able to deploy 7 more armies.

Advice will be gratefully received

if its turn 0 you cant deploy until turn 1 that could be the problem

Are you counting the comandeers?

No, we're on turn 6, and yes I'm counting the commandeers, of which I have 4.

Aha,

I have 2 castles! Just found the other one. Don't recall that being stated on the instructions. Now firing on all cylinders!

Look at your military screen. That should say "XXX of YY" armies which lets you know the maximum. Any messages to the contrary would be confusing to me as well.

I thought "double trouble" mode was gone. We got two castles for a number of months and then it went back to being just one, is there some exception to this?

beginner games are still double trouble