[quote=Titanic]
I got this event idea that I got to say. in the far future, a massive empire of tiny hamsters riding giant beast invade.Edit: Anyone want to discuss becoming trading partners? It would help to be close.Do I count militia's below 500 in the standing army?
[/quote]

Standing armies are the troops you always keep active, regardless of their type or quality. Over time, your country might look at updating its existing forces or expanding them. Either way, if an army comes marching across your lines, you'll naturally sound for a call to arms. Every eligible combatant will assemble at the nearest rally point, and militias will be formed. Within a couple of days your standing army could increase rapidly, but then I guess depending on how wealthy you are, the resources available and your nation's stance on training, the militias will be of varying quality and unreliable against a professional army. 

If you go on to defeat the attackers, and then you launch a counter-offensive over their border with an army of 40,000 soldiers, then I will start paying attention to what you're upto. It's all well and good having those soldiers, but if met with thick resistance and you're forced to lay siege, coffers are gonna start getting hurt. Just remember, you have to pay to keep your soldiers supplied, and you have to pay for their services UNLESS you promise them the loot from the besieged city. But then, razing a city and stealing its valuables wont make the occupied population like you very much. 

^^^ Just a few more of my thoughts on the subject.