How do I protect my troops?

Use the "Peace Shield" item to protect your city from being attacked for a period of time (does not protect troops outside the city).
Withdraw troops on the Resource Tile if they're being attacked.
Send out troops to avoid being attacked if your city is under attack.
Use "Advanced Teleport" items to flee from the chaos, and your enemy won't know about your new location for a while.
Build enough hospitals so that your troops will be wounded instead of being killed in battle. This way, you can return wounded troops to the battlefield in the shortest time and with the least resources possible.
An alliance is always a powerful form of insurance. Allies can send reinforcements to the Trading Post in your city. Your allies can support you more easily when you are located nearby.