My biggest military disaster is one I repeat often. I'll be merrily building my empire when all of a sudden I hear the horns. Someone has declared on me and I have neglected my army. All I can do is try my best to slow the AI down but the outcome is certain. One of my most memerable losses came at the hands of Isabella. I over expanded and my units had been disbanding. I was starting to turn the corner when a hugh stack came from the north. Her stack spread and was pillaging everthing in sight. Then she'd take a city. More pillaging then another city. I couldn't build units fast enough and with each city lost it got worse. That was one slow painful death. At least it gave me a feel for how much I can let my economy suffer before I have to fix it. Another bad military loss came from Napolean. I could see one of his coastal cities and noticed all the ships it was collecting. I had already experienced large French armies so I was eager to eliminate that threat. I built my army and navy. I put my army in a friendly civ on his continent. Moved it into position and declared. My army entered his territory and got close to its target city. Then came the counter attack. Went on for ages. All that effort just gone. I would say ' in a snap' but it was more like 15 minutes. What a waste of hammers. I won the game but when I see the French I always make it a point to beat them down early.