Number of warcasters?

[DannyBoy2k]

Now, granted I only have the 'original' Prime, and not the remix, but I sort of doubnt that this would be diffrent between them...

Having looked through the rules, I can't find anywhere it says you HAVE to have a full compliment of warcasters? Granted, a Duel would be sort of difficult without one, but any other size battle only states you MAY have up to X number of warcasters...not that you MUST? If I want to run a War with just the one and then a large number of support troops, that should be quite acceptable...and yet Army Builder screams if I have less, OR more than 3.