An early war when I was (a greatly oversized) Brandenburg with a few of the other HRE German states in my alliance, when another alliance in the HRE declared war on me, and there was a big mess of armies running all over the place. It was great when I mustered an army of almost 60,000 in one spot once... the biggest army I've ever made so early. It got less fun when Prussia declared independence though. ^_^